Regio- and stereoselective behavior of L -arabinal-derived vinyl epoxide 6.1 in nucleophilic addition reactions

CHAPTER 6

Regio- and stereoselective behavior of L -arabinal-derived vinyl epoxide 6.1 in nucleophilic addition reactions

6.1. Synthesis of the L -arabinal-derived vinyl epoxide 6.1

D

-Galactal- 1.1β and

-allal-derived vinyl epoxide 1.1α have been demonstrated to be excellent glycosyl donors in addition reactions of O- and C-nucleophiles, leading, through a complete 1,4- regio and syn-stereoselective process, to the exclusive obtainment of corresponding O- and C- glycosides having the same configuration (α or β) as the starting epoxide (α or β). The syn- stereoselective results had been razionalized by admitting the occurrence of an oxirane oxygen- nucleophile coordination, as previously discussed in the first part of this thesis (Chapter 1).

With azide ion (N-nucleophile) and thiols (S-nucleophiles) variable amounts of corresponding syn-1,4- and/or anti-1,2-addition products were obtained depending on the ability of the corresponding nucleophile to coordination.

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Scheme 6.1. D-Galactal- 1.1β and D-allal-derived vinyl epoxide 1.1α.

Actually, in epoxide 1.1β, which was shown to exist as the only conformer 1.1β’ with the side chain equatorial, the complete syn-stereoselective result obtained with alcohols and alkyl lithium compounds could be the consequence of a particularly favorable situation determined by the conformational rigidity of the system. In order to check, on one hand, if the presence of conformational effects could negatively influence the observed syn-stereoselectivity and, on the other hand, to validate our rationalization also in a mobile glycal-derived vinyl oxirane system, we directed our attention to

-arabinalal-derived vinyl epoxide 6.1. Actually epoxide 6.1 has the same absolute configuration as reference epoxide 1.1β and theoretical calculations have indicated that it exists as an equilibrium 81:19 of the two corresponding conformers 6.1’ and 6.1” in which the ring conformation of the major conformer 6.1’ corresponds to that of the unique conformer 1.1β’

present in the related 5-CH

OBn-substituted epoxide 1.1β.

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Scheme 6.2. Conformational equilibrium in vinyl epoxides 1.1β and 6.1.

Further interest in vinyl epoxide 6.1 derived from the fact that, if it would be a stereoselective glycosylating agent, it could be considered a valid and simple substrate for the completely stereoselective construction of alkyl 2,3-dideoxy-β-

-glycero-pent-2-enopyranosides. For these reasons, the unprecedented described epoxide 6.1 was synthesized and its regio- and stereoselective behavior examined in nucleophilic addition reactions under the same reaction conditions previously used for epoxide 1.1β.

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Scheme 6.3. Synthesis of L-arabinal-derived vinyl epoxide 6.1

.

Epoxide 6.1 was prepared starting from the known

-xylal 6.6, on its own prepared from

-xylol

6.2.

The treatment of

-xylal 6.6 with the encumbered TBSCl leads to the mono O-TBS derivative

6.7 which is transformed into mesylate 6.8 by MsCl/Py protocol. Deprotection of 6.8 by TBAF/THF procedure afforded trans hydroxy mesylate 6.9, the ultimate stable precursor of epoxide 6.1. Actually, epoxide 6.1 is not stable and can be prepared only in situ by base-catalyzed cyclization of trans hydroxy mesylate 6.9 and left to react immediately with the appropriate nucleophile.

6.2. Reaction of epoxide 6.1 with O-Nucleophiles

In the examination of the regio- and stereochemical behavior of the new

-arabinal-derived vinyl epoxide 6.1 with O-nucleophiles, the addition reactions with simple, low-boiling alcohols, such as MeOH, EtOH, i-PrOH, t-BuOH were examined under protocol A reaction conditions (alcohol as a solvent) (Table 6.1). The reactions turned out to be completely 1,4-regioselective, with the exclusive nucleophilic attack on the C(1) carbon of the vinyl system. No traces of corresponding 1,2-addition products were observed.

Table 6.1. Glycosylation of alcohols by epoxide 6.1 under protocols A and B.

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Entry O-nucleophile Reaction protocol β-O-glycoside α-O-glycoside

1 MeOH Protocol A

6.10β 47

R= Me 6.10α

53

2 Protocol B >99 <1

3 EtOH Protocol A

(-)-6.11β 69

R= Et (-)-6.11α 31

4 Protocol B >99 <1

5 i-PrOH Protocol A

6.12β 93

R= i-Pr 6.12α

7

6 Protocol B >99 <1

7 t-BuOH Protocol A

(-)-6.13β

>99

R= t-Bu 6.13α

-

8 BnOH Protocol B

(-)-6.14β

>99

R= Bn (-)-6.14α -

As for the stereoselectivity under protocol A, the reactions with the less nucleophilic and more sterically hindered t-BuOH, in spite of the presence of a large amount of nucleophilic molecules, is completely β-stereoselective with the exclusive formation of the corresponding t-butyl β-O- glycoside (-)-6.13β with the same configuration (β) as the starting epoxide. On the contrary, the reactions with the more nucleophilic MeOH, EtOH and i-PrOH are not stereoselective, and mixtures of the corresponding anomeric methyl 6.10α and 6.10β (55:45),

ethyl (-)-6.11α and (-)- 6.11β (31:69) and i-propyl O-glycosides 6.12α and 6.12β (7:93)

are obtained, respectively. Even if not completely stereoselective, it is worth noting that, in each mixture, with the exclusion of the less hindered and more nucleophilic MeOH, the corresponding β-anomer with the same configuration as the starting epoxide is the main product. However, in all cases, when the reactions are repeated under protocol B reaction conditions (only 3 equiv of alcohol in CH

CN as the solvent, Scheme 6.4), all the reactions become completely β-stereoselective and the corresponding β-O- glycosides 6.10β-6.13β are the only reaction products. Protocol B reaction conditions were necessarily used also in the glycosylation of benzyl alcohol, as an example of O-nucleophile for which protocol A reaction conditions are not reasonably possible. A complete β-stereoselective result was obtained with the exclusive formation of benzyl β-O-glycoside (-)-6.14β.

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Scheme 6.4. Glycosylation of alcohols by epoxide 6.1 under protocol B reaction conditions.

Also the possibility of the construction of a disaccharide by means of epoxide 6.1 was envisaged.

As a first approach, epoxide 6.1 was left to react with methyl O-glycoside 6.10β, as the O-

nucleophile, following the usual protocol B reaction conditions. Unexpectedly, no glycosylation

occurred and the unreacted methyl O-glycoside was the only compound recovered from the crude

reaction mixture. The same unsuccessful result was obtained also when the same reaction was

repeated by using

-galactal derived epoxide 1.1β, as the glycosyl donor. Considering that epoxide

1.1β

and now also epoxide 6.1 (Table 6.1) are excellent glycosyl donor toward primary, secondary

and tertiary alcohols, also not simple, the present negative results with methyl O-glycoside 6.10β (a

secondary alcohol) were not reasonable.

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Scheme 6.5. Unsuccessful attempts to synthesize 2,3-unsaturated-1,4-disaccharides by epoxides 6.1 and 1.1β and methyl O-glycoside 6.10β.

However, considering that previous studies on epoxide 1.1β had demonstrated that the same regio- and completely stereoselective glycosylation process obtained with alcohols could be realized also with the corresponding metal alcoholate, we decided to try this alternative glycosylation protocol.

Following the new procedure, the preformed lithium alcoholate 6.13β-Li obtained from t-butyl O- glycoside (-)-6.13β and LHMDS, was left to react with epoxide 6.1. A clean reaction occurred and the 2,3-unsaturated-β-O-1,4-disaccharide (-)-6.15 was obtained, as the only reation product.

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Scheme 6.6. Synthesis of 2,3-unsaturated-1,4-disaccharide 6.15.

Unsaturated disaccharide (-)-6.15 was acetylated (Ac

O/Py) to corresponding disaccharide 6.15-Ac

which was dihydroxylated by catalytic OsO

/NMO protocol. The dihydroxylation process occurred

in a completely stereoselective fashion by electrophilic attack exclusively on the α-face of the

molecule, that is in a direction opposed to the β-direction of the allyl substituents at C(1) and C(4)

of the two units of the unsaturated disaccharide (-)-6.15-Ac. In this way, the fully functionalized

acetylated disaccharide 6.16 was the only reaction product containing two units of

-lyxopyranose

through a 1,4-β-

-O-lyxopyranosidic bond.

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The same reaction was repeated on the

-galactal-derived epoxide 1.1β by using t-butyl-O- glycoside lithium salt 6.13β-Li. The reaction proceeded as expected and the mixed unsaturated β- 1,4-O-disaccharide 6.18 was the only product. Subsequent acetylation afforded the corresponding acetyl derivative (+)-6.18-Ac, which is our intention to dihydroxylate when a sufficient amount of the necessary starting material will be available (Scheme 6.8).

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Scheme 6.8. Synthesis of 2,3-unsaturated-1,4-disaccharide (+)-6.18-Ac.

The structure of disaccharide 6.16 was demonstrated by examination of the corresponding fully-

acetylated derivative (+)-6.17. The examination of the

H NMR spectra of this compound shows

the presence of small coupling constant values for the two anomeric protons H

and H

to indicate their equatorial nature and, as a consequence, the exact direction (α) of the dihydroxylation and glycosylation process (β), thus confirming the assigned structure.

6.3. Reactions of epoxide 6.1 with C-Nucleophiles

As C-nucleophiles, alkyl lithium compounds having differently hybridized nucleophilic carbon, as butyllithium (sp

), phenyllithium (sp

) and phenylacetylene (sp),

were examined (Scheme 6.9).

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Scheme 6.9. Reaction of vinyl epoxide 6.1 with C-nucleophiles.

In all cases, the glycosylation reaction turned out to be completely 1,4-regioselective and stereoselective leading only to the corresponding C-glycoside having the same configuration β as the starting epoxide (syn-1,4-addition product or coordination product).

In order to demonstrate its configuration, C-glycoside (-)-6.21 was dihydroxylated by OsO

/NMO to triol 6.24, as the only reaction product. The

H NMR spectrum of the tri-O-acetyl derivative (+)- 6.24-triAc showed for anomeric proton H

a large coupling constant value (J = 9.7 Hz) indicative of its axial nature and of a trans diaxial relationship with the adjacent H

proton in the more stable conformer (+)-6.24-triAc’ with the phenyl group equatorial. This type of relationship between H

and H

is possible only if the dihydroxylation had occurred selectively from the α-face of the starting unsaturated system, thus confirming the structure assigned to triol 6.24 and, as a consequence, to C-glycoside (-)-6.21 (Scheme 6.10).

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Scheme 6.10. Catalytic dihydroxilation of β-C-glycoside (-)-6.21.

The reaction with TMSCN is completely β-stereoselective affording O-TMS protected β-C- glycoside (+)-6.25.

This structure was confirmed by

H NMR analysis, in which a NOE was observed between H

and H

protons (Scheme 6.11).

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6.4. Reaction of epoxide 6.1 with N-Nucleophiles

In an attempt to synthesize N-glycosides by means of epoxide 6.1, the behavior of some N- nucleophiles as an amine and azide ion was examined. The reaction of epoxide 6.1 with propylamine (as the solvent/nucleophile, protocol A) was not useful to our aim because only the corresponding 1,2-addition product, the trans amino alcohol (+)-6.26, was obtained in a completely anti-stereoselective fashion (Scheme 6.12).

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Scheme 6.12. Reaction of vinyl epoxide 6.1 with PrNH2.

A corresponding regio- and stereoselective behavior was observed also with tetramethylguanidine

azide (TMGA) which, in spite of a certain tendency toward 1,4-addition shown in other epoxy-

glycal systems,

in the present case led to a complete 1,2-regio- and anti-stereoselectivity with the

exclusive formation of trans azido alcohol (+)-6.27 (Scheme 6.13).

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Scheme 6.13. Reaction of vinyl epoxide 6.1 with TMGA.

Decidedly different is the behavior of epoxide 6.1 with a further source of azide ion as TMSN

.

In this case, the examination of the crude reaction product showed the presence of an almost 1:1 mixture of an 1,2-addition product, not better identified and an 1,4-addition product (

H NMR).

Subsequent separation/purification of this mixture led to the recovering of only the 1,2-addition product which turned out to be the cis azido alcohol (-)-6.31. On the contrary, 1,4-addition product 6.29, initially present in the crude reaction mixture, was completely lost, not making the determination of its configuration possible (Scheme 6.14).

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Scheme 6.14. Reaction of vinyl epoxide 6.1 with TMSN3.

However, based on our previous experience on the azidolysis of glycal-derived epoxides with

TMSN

and considering that a vinyl epoxide as 6.1 cannot reasonably give a complete syn-

stereoselective opening process, and that two regioisomeric azido derivatives are present in the

crude reaction product even if only one, the syn-1,2-addition product, is obtained from the reaction,

we think that the 1,4-addition product present (

H NMR) in the crude reaction mixture corresponds

to β-azido glycoside 6.29. Actually, the β-azido glycoside 6.29 is the primary reaction product

which cannot be recovered from the reaction mixture because it rapidly isomerizes to cis-azido

alcohol (-)-6.31 (the secondary reaction product) by means of a suprafacial [3,3] sigmatropic

rearrangement. In other words, the reaction of epoxide 6.1 with TMSN

is completely 1,4-syn-

regioselective, but, unfortunately, the obtained β-azido-glycoside 6.29 (coordination product) is

not stable and isomerizes to the corresponding, more stable, syn-1,2-addition product (-)-6.31, with complete retention of configuration.

In a further attempt to synthesize a N-functionalized-glycoside, we thought that benzylcarbamate (BnOCONH

) could be an interesting nucleophile. Actually, benzylcarbamate presents sufficiently acid N-H bond for an easy deprotonation and once introduced, the –NHCOOBn residue could be used for the construction of N-glycoconjugates.

The reaction of epoxide 6.1 with the sodium salt of benzylcarbamate, separately prepared from BnOCONH

and NaHMDS, led, with our complete satisfaction, to the corresponding 1,4-addition product, the β-N-Cbz-glycoside (+)-6.32 having the same configuration as the epoxide: no trace of other regio- and/or diastereoisomer could be detected (

H NMR) in the crude product. N-glycoside (+)-6.32 turned out to be sufficiently stable to be purified by chromatographic procedures (Scheme 6.15).

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On the basis of this result, we wanted to verify if the same behavior could be observed also in epoxide 1.1β, bearing the C(5)-CH

OBn side-chain. The application of the above described protocol (CbzNH

/NaHMDS) to epoxide 1.1β determined the regio- and stereoselective glycosylation of benzylcarbammate with the exclusive formation of β-N-Cbz-glycoside (-)-6.33 (coordination product). The presence of a NOE between H

and anomeric H

protons confirmed the structure assigned to (-)-6.33, as shown in Scheme 6.16.

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6.5. Reaction of epoxide 6.1 with S-Nucleophiles

The reaction of epoxide 6.1 with PhSH, taken as a typical example of S-nucleophile, affords a 73:27 mixture of two regioisomeric products: the trans phenylthio alcohol (+)-6.34 (anti-1,2- addition product, non-coordination product) and phenylthio-glycoside 6.35, an 1,4-addition product, whose configuration was not possible to establish. If the formation of anti-1,2-addition product is easily justified by the neutral or slightly alkaline reaction conditions due the slight excess of t-BuOK, necessary for the formation of epoxide 6.1 from its precursor, the presence of a 1,4- addition product, probably the coordination product, could derive from the occurrence of a coordination (hydrogen bond) between the thiol (PhSH) and the oxirane oxygen, as arbitrarily shown in Scheme 6.17. The reduced ability of thiols to hydrogen bond with respect to alcohols is the reason why, in this case, the 1,4-addition product is only a minor component of the crude reaction product and not the main or unique product, as observed with alcohols.

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Scheme 6.17. Reaction of vinyl epoxide 6.1 with PhSH.

6.6. Conclusion

In conclusion, the results obtained with the mobile epoxide 6.1 are substantially similar to those

previously obtained with the conformationaly constrained epoxide 1.1β. This result clearly

indicates that the partial (some amounts of corresponding 1,2-addition products can be present, in

some cases) or complete 1,4-regioselectivity with complete syn-stereoselectivity (anti-1,4-addition

products are never obtained under protocol B reaction conditions) observed in glycal-derived

epoxides as 1.1β, 1.1α and 6.1 is independent of the presence of substituents on the six-membered

unsaturated ring and on the resulting conformational freedom: it depends only on the ability of the

nucleophile to give a coordination process with the oxirane oxygen in the form of a hydrogen bond

or through a coordinating metal.

6.7. Experimental

General Procedures. See Chapter 1.

Materials.

-(+)-Xylose, Ac

O, 33% HBr in AcOH, MeONa, 1.0 M NaHMDS in THF, 1.0 M LHMDS in THF, TBSCl, 1.0 M TBAF in THF, EtOH (absolute), phenol, PhSH, TMSCN, 1.6 M BuLi in hexane, 1.8 M PhLi in Et

O, MsCl, anhydrous MeCN over molecular sieves, anhydrous pyridina over molecular sieves, anhydrous DMF over molecular sieves, and t-BuOK were purchased from Aldrich and used without purification. MeOH, i-PrOH, and t-BuOH were distilled from calcium hydride at 760 Torr. Benzene, toluene, Et

O and THF were distilled from sodium/benzophenone.

-xylal 6.6,

epoxide 1.1β

and TMGA

were prepared as previously described.

Instrumentation. See Chapter 1.

Synthesis of trans hydroxy mesylate 6.9 (precursor of

-arabinal vinyl epoxide 6.1)

3-O-(t-Butyldimethylsilyl)-

-xylal (6.7)

A solution of

-xylal 6.6 (6.860 g, 59.10 mmol) in anhydrous DMF (152.6 mL) was treated with imidazole (6.430 g, 94.56 mmol, 1.6 equiv) and TBSCl (9.760 g, 65.0 mmol, 1.1 equiv) at 0°C and the reaction mixture was stirred 24 h at room temperature. Dilution with CH

Cl

and evaporation of the washed (saturated aqueous NaCl) organic solvent afforded a crude product (10.22 g, 76% yield) consisting of practically pure TBS-derivative 6.7, as a brown liquid, which was used in the next step without any further purification. An analytical sample of crude 6.7 was purified by flash chromatography. Elution with an 8:2 hexane/AcOEt mixture afforded pure alcohol 6.7.

6.7: a liquid: R

= 0.58 (6:4 hexane/AcOEt);

H NMR (CDCl

) δ 6.45 (d, 1H, J =6.1 Hz), 4.79 (ddd, 1H, J= 6.5, 4.7, 1.4 Hz), 3.96-4.02 (m, 2H), 3.87-3.95 (m, 1H), 3.66- 3.72 (m, 1H), 0.88 (s, 9H), 0.09 (s, 6H).

3-O-(t-Butyldimethylsilyl)-4-O-mesyl-

-xylal (6.8)

A solution of the alcohol 6.7 (10.0 g, 43.47 mmol) in a 1:1 mixture of anhydrous CH

Cl

(47.0 mL) anhydrous pyridine (47.0 mL) was treated dropwise at 0°C with MsCl (6.7 mL, 86.94 mmol, 2.0 equiv) and the reaction mixture was stirred 18 h at the same temperature. Dilution with Et

O and evaporation of the washed (brine) organic solvent afforded a crude product (8.0 g, 60% yield) consisting of mesylate 6.8, practically pure, as a brown liquid, which was used in the next step

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without any further purification. An analytical sample of crude 6.8 was subjected to flash chromatography. Elution with an 8:2 hexane/AcOEt mixture afforded pure mesylate 6.8.

6.8: a yellow liquid; R

= 0.63 (6:4 hexane/AcOEt).

H NMR (CDCl

) δ 6.47 (dd, 1H, J= 6.3, 0.4 Hz), 4.81 (ddd, 1H, J= 4.6, 1.4 Hz), 4.60-4.66 (m, 1H), 4.20 (ddd, 1H, J= 12.1, 1.4 Hz), 4.10-4.15 (m, 1H), 4.09 (dd, 1H, J= 12.1, 1.8 Hz), 3.07 (s, 3H), 0.88 (s, 9H), 0.12 (s, 3H), 0.11 (s, 3H).

C NMR (CDCl

) δ 145.8, 101.3, 76.0, 63.4, 62.3, 38.9, 25.9, 18.1, -4.26, -4.47.

4-O-mesyl-

-xylal (6.9)

A solution of mesylate 6.8 (2.0 g, 6.49 mmol) in anhydrous THF (200.0 mL) was treated at 0°C with 1M TBAF in THF (6.49 mL, 6.49 mmol, 1.0 equiv). After 40 minutes stirring at the same temperature, dilution with Et

O and evaporation of the washed (brine) organic solution afforded a crude product (1.0 g) consisting of trans hydroxy mesylate 6.9 which was purified by flash chromatography. Elution with a 4:6 hexane/AcOEt mixture afforded pure 6.9 (0.508 g, 40% yield).

6.9: a colorless liquid; R

= 0.08 (6:4 hexane/AcOEt).

H NMR (CDCl

) δ 6.53 (d, 1H, J= 6.2 Hz), 4.89-4.98 (m, 1H), 4.71-4.80 (m, 1H), 4.20-4.27 (m, 1H), 4.15-4.19 (m, 1H), 4.10 (dd, 1H, J = 12.3, 2.5 Hz), 3.11 (s, 3H).

C NMR (CDCl

) δ 146.9, 100.4, 75.8, 63.6, 62.6, 38.8.

Glycosylation of alcohols (O-nucleophiles) by vinyl epoxide 6.1 Reaction of epoxide 6.1 with MeOH (Protocol A)

Typical procedure. A solution of trans hydroxy mesylate 6.9 (0.080 g, 0.41 mmol) in anhydrous MeOH (3.0 mL) was treated with t-BuOK (0.090 g, 0.82 mmol, 2.0 equiv) and the reaction mixture was stirred at room temperature for 12 h. Dilution with Et

O and evaporation of the washed (brine) organic layer afforded a crude product (0.040 g) consisting of a 47:53 mixture of methyl α-O- glycoside 6.10α and methyl β-O-glycoside 6.10β (

H NMR) which was subjected to preparative TLC (a 4:6 hexane/AcOEt mixture was used as the eluant). Extraction of the two most intense bands (the faster moving band contained 6.10β) afforded pure methyl α-O-glycoside 6.10α (0.007 g, 14% yield) and methyl β-O-glycoside 6.10β (0.008 g, 16% yield):

Methyl 2,3-dideoxy-β-

-glycero-pent-2-enopyranoside (6.10β): a liquid, R

= 0.38 (4:6 hexane/AcOEt).

H NMR (CDCl

) δ 5.94-6.04 (m, 1H), 5.69-5.81 (m, 1H), 4.82 (bs, 1H), 4.12-4.30 (m, 1H), 3.80 (dd, 1H, J = 10.7, 5.3 Hz), 3.61-3.73 (m, 1H), 3.45 8 (s, 3H).

C NMR (CDCl

) δ 133.2, 127.9, 95.9, 64.1, 63.3, 56.1.

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Methyl 2,3-dideoxy-α-

-glycero-pent-2-enopyranoside (6.10α): a liquid, R

= 0.26 (4:6 hexane/AcOEt).

H NMR (CDCl

) δ 6.07-6.17 (m, 1H), 5.87 (dd, 1H, J = 10.0, 3.1 Hz), 4.80-4.84 (m, 1H), 4.08 (dd, 1H, J = 12.0, 2.5 Hz), 3.73-3.84 (m, 1H), 3.42 (s, 3H).

C NMR (CDCl

) δ 129.4, 128.5, 94.4, 64.4, 61.7, 55.8.

Reaction of epoxide 6.1 with MeOH in benzene (Protocol B)

Typical procedure. A solution of trans hydroxy mesylate 6.9 (0.060 g, 0.31 mmol) in anhydrous benzene (3.2 mL) was treated with t-BuOK (0.035 g, 0.31 mmol, 1.0 equiv) and the reaction mixture was stirred 20 minutes at room temperature. Cyclization was monitored by TLC analysis and after desappearance of the starting material, MeOH (0.04 mL, 0.93 mmol, 3.0 equiv) was added to the reaction mixture and stirring was prolonged for 1 h. Dilution with Et

O and evaporation of the washed (brine) organic phase afforded methyl β-O-glycoside 6.10β (0.015 g, 38% yield), as the only reaction product, pure as a yellow liquid.

Reaction of epoxide 6.1 with EtOH (Protocol A)

Following the typical procedure, the treatment of the trans hydroxy mesylate 6.9 (0.094 g, 0.49 mmol) in anhydrous EtOH (3.5 mL) with t-BuOK (0.109 g, 0.98 mmol, 2.0 equiv) afforded, after 1 h at room temperature, a 69:31 mixture of ethyl α-O-glycoside (-)-6.11α and ethyl β-O-glycoside (-)-6.11β (

H NMR) which was subjected to preparative TLC (a 4:6 hexane/AcOEt mixture was used as the eluent). Extraction of the most intense bands (the faster moving band contained (-)- 6.11β) afforded pure ethyl α-O-glycoside (-)-6.11α (0.009 g, 13% yield) and ethyl β-O-glycoside (-)-6.11β (0.055 g, 78% yield):

Ethyl 2,3-dideoxy-β-

-glycero-pent-2-enopyranoside (-)-(6.11β): a liquid, R

= 0.41 (4:6 hexane/AcOEt); [α]

-34.57 (c 1.62, CHCl

).

H NMR (CDCl

) δ 5.95-6.06 (m, 1H), 5.77 (ddd, 1H, J = 10.2, 2.4, 1.8 Hz), 4.89-4.95 (m, 1H), 4.09- 4.29 (m, 1H), 3.64-3.94 (m, 3H), 3.47-3.62 (m, 1H), 1.24 (t, 3H, J = 7.1 Hz).

C NMR (CDCl

) δ 133.0, 128.2, 94.6, 64.3, 64.1, 63.3, 15.5.

Ethyl 2,3-dideoxy-α-

-glycero-pent-2-enopyranoside (-)-(6.11α): a liquid, R

= 0.29 (4:6 hexane/AcOEt); [α]

-72.5 (c 0.52, CHCl

).

H NMR (CDCl

) δ 6.08-6.17 (m, 1H), 5.89 (ddd, 1H, J = 10.1, 3.6, 0.4 Hz), 4.95 (dd, 1H, J = 3.0, 0.4 Hz), 4.12 (dd, 1H, J = 12.2, 2.6 Hz), 3.73-3.91 (m, 3H), 3.46-3.62 (m, 1H), 1.23 (t, 3H, J = 7.1 Hz).

C NMR (CDCl

) δ 129.3, 128.8, 93.2, 64,4, 63.9, 61.7, 15.4.

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Reaction of epoxide 6.1 with EtOH in benzene (Protocol B)

Following the typical procedure, the treatment of trans hydroxy mesylate 6.9 (0.034 g, 0.18 mmol) in anhydrous benzene (2.3 mL) with t-BuOK (0.020 g, 0.18 mmol, 1.0 equiv) and EtOH (0.031 mL, 0.54 mmol, 3.0 equiv), afforded, after 15 minutes stirring, a crude product (

H NMR) consisting of ethyl β-O-glycoside (-)-6.11β (0.020 g, 79% yield).

Reaction of epoxide 6.1 with i-PrOH (Protocol A)

Following the typical procedure, the treatment of the trans hydroxy mesylate 6.9 (0.028 g, 0.14 mmol) in anhydrous i-PrOH (1.0 mL) with t-BuOK (0.031 g, 0.28 mmol, 2.0 equiv) afforded, after 1 h at room temperature, a 7:93 mixture of isopropyl α-O-glycoside 6.12α and isopropyl β-O- glycoside 6.12β (

H NMR) (0.022 g, 90% yield).

i-Propyl 2,3-dideoxy-β-^L

-glycero-pent-2-enopyranoside (6.12β): R

= 0.42 (4:6 hexane/AcOEt).

H NMR (CDCl

) δ 5.99 (ddd, 1H, J = 10.2, 1.2 Hz), 5.72 (ddd, 1H, J = 10.2, 1.7 Hz), 4.98-5.03 (m, 1H), 4.13-4.28 (m, 1H), 3.98 (eptet, 1H, J = 6.2 Hz), 3.77 (ddd, 1H, J = 11.0, 5.5, 0.8 Hz), 3.69 (dd, 1H, J = 11.0, 8.0 Hz), 1.23 (d, 3H, J = 6.2 Hz), 1.16 (d, 3H, J = 6.2 Hz).

C NMR (CDCl

) δ 133.0, 128.4, 92.8, 70.4, 63.7, 63.3, 23.8, 22.0.

Reaction of epoxide 6.1 with i-PrOH in benzene (Protocol B)

Following the typical procedure, the treatment of trans hydroxy mesylate 6.9 (0.025 g, 0.13 mmol) in anhydrous benzene (1.6 mL) with t-BuOK (0.014 g, 0.13 mmol, 1.0 equiv) and i-PrOH (0.030 mL, 0.39 mmol, 3.0 equiv), afforded, after 2 h stirring, a crude product (

H NMR) consisting of isopropyl β-O-glycoside 6.12β (0.015 g, 76% yield).

Reaction of epoxide 6.1 with t-BuOH (Protocol A)

Following the typical procedure, the treatment of the trans hydroxy mesylate 6.9 (0.028 g, 0.14 mmol) in anhydrous t-BuOH (1.0 mL) with t-BuOK (0.031 g, 0.28 mmol, 2.0 equiv) afforded, after 1 h at room temperature, a crude product consisting of t-butyl β-O-glycoside (-)-6.13β (0.024 g, 90% yield), as the only reaction product, pure as a pale yellow liquid.

t-Butyl 2,3-dideoxy-β-L

-glycero-pent-2-enopyranoside (-)-(6.13β): R

= 0.50 (4:6 hexane/AcOEt); [α]

-57.28 (c 1.36, CHCl

).

H NMR (CDCl

) δ 5.97 (d, 1H, J = 10.3 Hz), 5.57-5.74 (m, 1H), 5.10-5.22 (m, 1H), 4.08-4.22 (m, 1H),

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3.64-3.85 (m, 2H), 1.25 (s, 9H).

C NMR (CDCl

) δ 132.4, 129.9, 88.4, 75.4, 64.1, 63.2, 28.9.

Reaction of epoxide 6.1 with BnOH in benzene (Protocol B)

Following the typical procedure, the treatment of trans hydroxy mesylate 6.9 (0.025 g, 0.13 mmol) in anhydrous benzene (1.6 mL) with t-BuOK (0.014 g, 0.13 mmol, 1.0 equiv) and BnOH (0.040 mL, 0.39 mmol, 3.0 equiv), afforded, after 2 h stirring, a crude product (

H NMR) consisting of benzyl β-glycoside 6.14β (0.045 g), which was subjected to preparative TLC (a 7:3 hexane/AcOEt mixture was used as the eluent). Extraction of the slower moving band afforded pure benzyl β-O- glycoside (-)-6.14β (0.003 g, 10% yield).

Benzyl 2,3-dideoxy-β-

-glycero-pent-2-enopyranoside (-)-(6.14β): R

= 0.35 (7:3 hexane/AcOEt); [α]

-12.56 (c 0.39, CHCl

).

H NMR (CDCl

) δ 7.27- 7.53 (m, 5H), 5.99-6.07 (m, 1H), 5.76-5.87 (m, 1H), 4.99-5.06 (m, 1H), 4.82 (d, 1H, J = 11.8 Hz), 4.58 (d, 1H, J = 11.8 Hz), 4.26-4.33 (m, 1H), 3.84 (ddd, 1H, J

= 10.8, 5.3, 0.7 Hz), 3.74 (dd, 1H, J = 10.8, 8.1 Hz).

C NMR (CDCl

) δ 137.9, 133.3, 128.6, 128.2, 128.0, 127.9, 93.7, 70.2, 63.9, 63.4.

Reaction of epoxide 6.1 with lithium salt of t-butyl β-O-glycoside (-)-6.13β (Protocol B) Formation of the lithium alcoholate of t-butyl β-O-glycoside (-)-6.13β (Solution A). A solution of t- butyl β-O-glycoside (-)-6.13β (0.039 g, 0.228 mmol, 1.8 equiv) in anhydrous THF (0.5 mL) was treated with a 1M LHMDS in hexane (0.023 mL, 0.228 mmol, 1.8 equiv) at -78°C and the reaction mixture was stirred for 1 h at the same temperature.

Formation of epoxide 6.1 (Solution B). Following the previously described procedure, a solution of trans hydroxy mesylate 6.9 (0.025 g, 0.128 mmol) in anhydrous THF (0.5 mL) was treated with t- BuOK (0.018 g, 0.154 mmol, 1.2 equiv) and the reaction stirred for 15 minutes until cyclization to epoxide 6.1 was achieved. After that, Solution A was added dropwise and the resulting reaction mixture was stirred overnight. Typical workup afforded a crude product (0.055 g) consisting of 1,4- β-O-disaccharide 6.15, which was subjected to preparative TLC, using a 1:1 hexane/AcOEt mixture as the eluant. Extraction of the most intense band afforded 1,4-β-O-disaccharide (-)-6.15 (0.022 g, 62% yield) pure as a colorless liquid.

t-Butyl

4-(2’,3’-dideoxy-β-

-glycero-pent-2’-enopyranosyl)-2,3- dideoxy-β-

-glycero-pent-2-enopyranoside (-)-(6.15): R

= 0.26 (1:1 hexane/AcOEt); [α]

-60.3 (CHCl

c 0.76);

H NMR (CDCl

) δ 5.91-

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6.05 (m, 2H), 5.71-5.79 (m, 1H), 5.63-5.70 (m, 1H), 5.18 (bs, 1H), 5.06 (bs, 1H), 4.19-4.31 (m, 2H), 3.73-3.87 (m, 3H), 3.65 (dd, 1H, J= 11.7, 8.5 Hz), 1.28 (s, 9H).

C NMR (CDCl

) δ 133.4, 130.5, 129.3, 127.8, 94.2, 88.6, 70.0, 63.7, 63.3, 61.3, 29.9, 28.9.

Acetylation of disaccharide (-)-6.15

1,4-β-O-disaccharide (-)-6.15 (0.019 g, 0.07 mmol) was dissolved in anhydrous pyridine (0.2 mL) and then treated with Ac

O (0.1 mL) at 0°C and the resulting reaction mixture was stirred at room temperature overnight. Co-evaporation of the reaction mixture with toluene afforded a crude product (0.022 g, >99% yield) consisting of (-)-6.15-Ac as a pale yellow liquid.

t-Butyl

4-[4’-O-(acetyl)-2’,3’-dideoxy-β-

-glycero-pent-2’- enopyranosyl]-2,3-dideoxy-β-

-glycero-pent-2-enopyranoside (-)- (6.15-Ac): R

= 0.63 (1:1 hexane/AcOEt); [α]

-63.1 (CHCl

c 0.56);

1

H NMR (CDCl

) δ 5.90-5.99 (m, 2H), 5.83 (ddd, 1H, J= 10.3, 2.3, 1.7 Hz), 5.67 (ddd, 1H, J= 10.3, 2.7, 2.0 Hz), 5.23-5.34 (m, 1H), 5.17 (bs, 1H), 5.08 (bs, 1H), 4.19-4.32 (m, 1H), 3.71-3.89 (m, 4H), 2.06 (s, 3H), 1.26 (s, 9H).

C NMR (CDCl

) δ 170.7, 130.7, 130.5, 129.4, 129.1, 94.0, 88.6, 70.0, 65.1, 61.3, 60.0, 29.9, 28.9, 21.2.

Dihydroxylation of disaccharide (-)-6.15-Ac

A solution of disaccharide (-)-6.15-Ac (0.022 g, 0.070 mmol) in an 1:1 t-BuOH/acetone mixture (0.03 mL) was added, at 0°C under stirring and in the dark, to a 50% p/v aqueous solution of N- methyl morpholine-N-oxide (NMO) (0.06 mL) and the resulting reaction mixture was treated with 2.5% p/v OsO

solution in t-BuOH (0.06 ml) and stirred for 96 h at room temperature. Dilution with Et

O and evaporation of the filtered (Celite

) organic solution afforded disaccharide 6.16 (0.029 g, >99% yield), practically pure as a liquid, which was subsequent acetylated following the typical procedure: a solution of disaccharide 6.16 (0.029 g, 0.076 mmol) in anhydrous pyridine (0.2 mL) was treated with Ac

O (0.1 mL) at 0°C and the resulting reaction mixture was stirred at room temperature overnight. Co-evaporation of the reaction mixture with toluene afforded a crude product (0.036 g, >99% yield) consisting of the disaccharide (+)-6.17, pure as a pale yellow liquid.

t-Butyl 4-O-(2’,3’,4’-tri-O-acetyl-β-^L

-lyxopyranosyl)-2,3-di-O- acetyl-β-

-lyxopyranoside (+)-(6.17): R

= 0.22 (1:9 hexane/AcOEt); [α]

+16.5 (c 0.21, CHCl

);

H NMR (CDCl

) δ 5.31 (dd, 1H, J = 9.7, 3.0 Hz), 5.30 (dd, 1H, J = 9.4, 3.3 Hz), 5.10-5.21 (m, 1H), 5.07 (t, 1H, J = 3.0 Hz), 5.02 (dd, 1H, J = 3.3, 2.0 Hz), 4.97 (d, 1H, J = 2.0 Hz), 4.92 (d, 1H, J = 3.0 Hz), 3.96-4.08 (m, 1H), 3.87 (dd, 1H, J =

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11.0, 8.9 Hz), 3.86 (dd, 1H, J = 10.7, 8.3 Hz), 3.75 (dd, 1H, J = 10.7, 6.4 Hz), 3.64 (dd, 1H, J = 11.0, 9.2 Hz), 2.12 (s, 3H), 2.11 (s, 3H), 2.07 (s, 3H), 2.05 (s, 3H), 2.04 (s, 3H), 2.03 (s, 3H).

C NMR (CDCl

) δ 171.1, 170.7, 170.4, 170.3, 170.1, 98.9, 92.4, 73.2, 71.8, 70.8, 69.7, 68.2, 67.2, 61.0, 60.5, 29.9, 28.6, 21.0.

Reaction of epoxide 1.1β with lithium salt of t-butyl β-O-glycoside (-)-6.13β (Protocol B) Formation of the lithium alcoholate of t-butyl β-O-glycoside (-)-6.13β (Solution A). A solution of t- butyl β-O-glycoside (-)-6.10β (0.050 g, 0.290 mmol, 1.8 equiv) in anhydrous THF (0.6 mL) was treated with a 1M LHMDS in hexane (0.29 mL, 0.290 mmol, 1.8 equiv) at -78°C and the reaction mixture was stirred for 1 h at the same temperature.

Formation of epoxide 1.1β (Solution B). Following the previously described procedure, a solution of trans hydroxy mesylate 1.3β (0.050 g, 0.160 mmol) in anhydrous THF (0.6 mL) was treated with t-BuOK (0.022 g, 0.190 mmol, 1.2 equiv) and the reaction stirred for 15 minutes until cyclization to epoxide 1.1β. After that, Solution A was added dropwise and the resulting reaction mixture was stirred overnight. Typical workup afforded a crude product (0.070 g) consisting of 1,4- β-O-disaccharide 6.18, which was dissolved in anhydrous pyridine (0.6 mL) and then treated with Ac

O (0.3 mL) at 0°C and the resulting reaction mixture was stirred at room temperature overnight.

Co-evaporation of the reaction mixture with toluene afforded a crude product (0.088 g, >99%

yield) consisting of (-)-6.18-Ac, which was subjected to preparative TLC, using a 1:1 hexane/AcOEt mixture as the eluant. Extraction of the most intense band afforded 1,4-β-O- disaccharide (-)-6.18-Ac (0.054 g, 78% yield), pure as a colorless liquid.

t-Butyl

4-[6’-O-(benzyl)-2’,3-dideoxy-β-

-threo-hex-2’- enopyranosyl)-2,3-dideoxy-β-

-glycero-pent-2-enopyranoside (-)-(6.18-Ac): R

= 0.26 (1:1 hexane/AcOEt); [α]

-74.8 (CHCl

c 0.18);

H NMR (CDCl

) δ 7.27-7.39 (m, 5H), 6.08 (dd, 1H, J = 9.6, 4.0 Hz), 6.00 (d, 1H, J = 9.9 Hz), 5.91 (d, 1H, J = 9.6 Hz), 5.68 (ddd, 1H, J = 9.9, 2.2, 1.8 Hz), 5.23 (bs, 1H), 5.17 (d, 1H, J = 2.2 Hz), 5.05-5.10 (m, 1H), 4.59 (d, 1H, J = 12.2 Hz), 4.48 (d, 1H, J

= 12.2 Hz), 4.32-4.43 (m, 1H), 3.93-4.01 (m, 1H), 3.85 (d, 2H, J = 7.4 Hz), 3.62 (dd, 1H, J = 6.2, 1.0 Hz), 1.99 (s, 3H), 1.26 (s, 9H).

C NMR (CDCl

) δ 171.7, 138.2, 132.9, 130.6, 129.5, 128.6, 127.9, 97.0, 88.6, 79.2, 73.7, 72.9, 69.7, 69.0, 64.0, 61.2, 28.9, 21.0.

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Reactions of epoxides 6.1 with C-Nucleophiles (protocol B) Reaction of epoxide 6.1 with PhLi

Typical procedure. A solution of trans hydroxy mesylate 6.9 (0.040 g, 0.206 mmol) in anhydrous Et

O (2.0 mL) was treated with t-BuOK (0.023 g, 0.247 mmol, 1.2 equiv). After 15 minutes stirring at room temperature, TLC analysis showed that the starting material was consumed by cyclization to epoxide 6.1. PhLi (0.108 mL, 0.206 mmol, 1.0 equiv) was added and stirring was prolonged at the same temperature for 2 h. Dilution with Et

O and evaporation of the washed (brine) organic solution afforded a crude reaction product (0.042 g) consisting of β-C-glycoside (-)-6.21 which was subjected to preparative TLC (a 7:3 hexane/AcOEt mixture was used as the eluant for 2 runs).

Extraction of the slower moving band afforded (-)-6.21 (0.025 g, 75% yield), pure as a colorless liquid.

(2R, 5R)-2-phenyl-5-hydroxy-5,6-dihydro-2H-pyrane (-)-(6.21): R

= 0.33 (4:6 hexane/AcOEt); [α]

-70.0 (c 0.44, CHCl

);

H NMR (CDCl

) δ 7.56-7.64 (m, 1H), 7.29-7.49 (m, 4H), 6.13 (ddd, 1H, J = 10.2, 4.9, 1.3 Hz), 5.99 (ddd, 1H, J = 10.2, 1.5, 0.4 Hz), 5.03-5.08 (m, 1H), 4.07 (dt, 1H, J = 11.9, 1.5 Hz), 3.95-4.03 (m, 1H), 3.88 (dd, 1H, J = 11.9, 2.3 Hz).

C NMR (CDCl

) δ 140.1, 131.5, 128.9, 128.8, 128.4, 127.4, 127.0, 76.9, 70.9, 62.4.

Dihydroxylation of the methoxy derivative 6.21

A solution of β-C-glycoside 6.21 (0.020 g, 0.114 mmol) in an 1:1 t-BuOH/acetone mixture (0.3 mL) was added, at 0°C under stirring and in the dark, to a 50% p/v aqueous solution of N-methyl morpholine-N-oxide (NMO) (0.01 mL) and the resulting reaction mixture was treated with 2.5%

p/v OsO

solution in t-BuOH (0.01 ml) and stirred for 96 h at room temperature. Dilution with Et

O and evaporation of the filtered (Celite

) organic solution afforded triol (6.24) (0.015 g, 63%

yield), practically pure as a liquid, which was dissolved in anhydrous pyridine (0.4 mL) and then treated with Ac

O (0.2 mL) at 0°C and the resulting reaction mixture was stirred at room temperature overnight. Co-evaporation of the reaction mixture with toluene afforded a crude product (0.022 g, 58% yield) consisting of (+)-6.24-triAc as a pale yellow liquid.

(2S,3S,4R,5S)-3,4,5-tri-acetoxy-2-phenyltetrahydro-2H-pyrane

(+)-(6.24-triAc): R

= 0.17 (1:1 hexane/AcOEt); [α]

+19.8 (c 0.76, CHCl

);

1

H NMR (CDCl

) δ 7.27-7.48 (m, 5H), 5.41 (t, 1H, J= 3.4 Hz), 5.30 (dd, 1H, J=

9.7, 3.4 Hz), 4.91-4.96 (m, 1H), 4.60 (d, 1H, J= 9.7 Hz), 4.01 (d, 2H, J= 1.8 Hz), 2.35 (s, 3H), 2.20 (s, 3H), 2.19 (s, 3H).

C NMR (CDCl

) δ 170.0, 169.6, 169.4, 137.5, 128.9, 128.7, 128.5, 127.3, 76.5, 69.5, 69.4, 67.5, 65.9, 21.2, 21.1, 20.7.

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Reaction of epoxide 6.1 with BuLi

Following the typical procedure, the treatment of trans hydroxy mesylate 6.9 (0.032 g, 0.166 mmol) in anhydrous Et

O (1.8 mL) with t-BuOK (0.018 g, 0.199 mmol, 1.2 equiv) and BuLi (0.42 mL, 0.664 mmol, 4.0 equiv) afforded, after 30 minutes stirring, a crude liquid product (0.029 g) consisting of β-C-glycoside (-)-6.22 which was subjected to preparative TLC, using a 1:1 hexane/AcOEt as the eluant. Extraction of the most intense band afforded (-)-6.22 (0.013 g, 50%

yield), pure as a liquid.

(2R, 5R)-2-butyl-5-hydroxy-5,6-dihydro-2H-pyrane (-)-(6.22): R

= 0.35 (4:6 hexane/AcOEt); [α]

-16.0 (c 1.3, CHCl

);

H NMR (CDCl

) δ 5.92-6.04 (m, 1H), 5.83 (dd, 1H, J= 10.3, 1.2 Hz), 3.94-4.04 (m, 2H), 3.82-3.92 (m, 1H), 3.68 (dd, 1H, J= 11.8, 2.2 Hz), 1.21-1.69 (m, 6H), 0.91 (t, 3H, J= 6.9 Hz).

C NMR (CDCl

) δ 134.6, 126.5, 74.9, 71.1, 62.9, 34.94, 27.4, 22.9, 14.2.

Reaction of epoxide 6.1 with PhCLi

Formation of the lithium phenylacetylide salt (Solution A). A solution of phenylacetylene (0.023 mL, 0.216 mmol, 1.4 equiv) in anhydrous THF (1.0 mL) was treated with BuLi (0.11 mL, 0.180 mmol, 1.2 equiv) and the reaction mixture was stirred for 1h.

Formation of epoxide 6.1 (Solution B). Following the previously described procedure, a solution of trans hydroxy mesylate 6.9 (0.030 g, 0.15 mmol) in anhydrous THF (1.6 mL) was treated with t- BuOK (0.020 g, 0.185 mmol, 1.2 equiv) and the reaction stirred until cyclization to epoxide 6.1 was achieved. After that, Solution A was added dropwise and the resulting reaction mixture was stirred 4 h. Typical workup afforded a crude product consisting of β-C-glycoside (-)-6.23 (0.032 g,

>99% yield), pure as a colorless liquid.

(2R, 5R)-2-phenylethynyl-5-hydroxy-5,6-dihydro-2H-pyrane (-)-(6.23):

R

= 0.50 (4:6 hexane/AcOEt); []

-13.7 (c 1.0, CHCl

).

H NMR (CDCl

) δ 7.45-7.54 (m, 2H), 7.27-7.37 (m, 3H), 5.99 (dd, 1H, J= 10.3, 2.5 Hz), 5.66 (dt, 1H, J= 10.3, 2.2 Hz), 5.19 (d, 1H, J= 2.5 Hz), 4.11-4.21 (m, 1H), 3.78 (d, 1H, J= 1.5 Hz), 3.75 (d, 1H, J= 3.4 Hz).

H NMR (CDCl

) δ 132.3, 129.9, 128.9, 128.5, 122.3, 89.5, 83.8, 64.1, 63.3.

Reaction of epoxide 6.1 with TMSCN

Following the typical procedure, the treatment of trans hydroxy mesylate 6.9 (0.040 g, 0.206 mmol) in anhydrous CH

CN (1.0 mL) with t-BuOK (0.028 g, 0.247 mmol, 1.2 equiv) and TMSCN

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(0.11 mL, 0.80 mmol, 4.0 equiv) afforded, after 30 minutes stirring, a crude liquid product (0.029 g) consisting of β-cyano-glycoside (+)-6.25 which was subjected to preparative TLC, using a 1:1 hexane/AcOEt as the eluant. Extraction of the most intense band afforded (+)-6.25 (0.025 g, 89%

yield), pure as a liquid.

4-O-Trimethylsilyl-2,3-dideoxy-β-

-glycero-pent-2-enopyranosyl cyanide (+)-(6.25): R

= 0.26 (6:4 hexane/AcOEt); [α]

+45.4 (c 0.27, CHCl

).

H NMR (CDCl

) δ 5.99 (ddd, 1H, J = 10.7, 3.2, 1.5 Hz), 5.72 (ddd, 1H, J = 10.7, 3.2, 1.8 Hz), 4.89 (dd, 1H, J = 5.5, 2.4 Hz), 4.24-4.36 (m, 1H), 3.93 (dd, 1H, J

= 11.2, 5.5 Hz), 3.53 (dd, 1H, J = 11.2, 8.7 Hz), 0.13 (s, 9H).

C NMR (CDCl

) δ 134.7, 128.1, 122.7, 121.7, 67.3, 65.4, 61.5, 29.9, 0.1.

Reactions of epoxides 6.1 with N-Nucleophiles (protocol B) Reaction epoxide 6.1 with TMGA

A solution of trans hydroxy mesylate 6.9 (0.050 g, 0.258 mmol) in anhydrous CH

CN (2.5 mL) was treated t-BuOK (0.029 g, 0.308 mmol, 1.2 equiv) and the reaction mixture was stirred 15 minutes. After cyclization to epoxide 6.1, TMGA (0.118 g, 0.774 mmol, 3.0 equiv) was added and the resulting mixture was stirred overnight. Dilution with Et

O and evaporation of the washed (brine) organic solution afforded a crude reaction product, consisting of trans azido alcohol (+)- 6.27 (0.023 g, 64% yield), pure as a yellow liquid.

3-Azido-3-deoxy-

-lyxal (+)-(6.27): R

= 0.60 (4:6 hexane/AcOEt); [α]

+146.9 (c 2.6, CHCl

).

H NMR (CDCl

) δ 6.59 (d, 1H, J = 6.1 Hz), 4.81 (t, 1H, J = 6.1 Hz), 3.99 (dd, 1H, J = 11.3, 4.4 Hz), 3.91 (dd, 1H, J = 11.3, 2.2 Hz), 3.72-3.85 (m, 2H);

13

C NMR (CDCl

) δ 147.7, 95.9, 66.8, 66.6, 56.3.

Reaction epoxide 6.1 with TMSN

A solution of trans hydroxy mesylate 6.9 (0.040 g, 0.206 mmol) in anhydrous CH

CN (1.0 mL) was treated with t-BuOK (0.028 g, 0.247 mmol, 1.2 equiv) and stirred 15 minutes. After cyclization to epoxide 6.1 was achieved (TLC), TMSN

(0.11 mL, 0.80 mmol, 4.0 equiv) was added and the resulting reaction mixture was stirred overnight. Dilution with Et

O and evaporation of the washed (brine) organic solution afforded a crude (0.048 g) consisting of a 60:40 mixture of β-N-glycoside 6.29 and cis 1,2-azido derivative (-)-6.31, which was subjected tu preparative TLC, using a 7:3 hexane/AcOEt mixture as the eluant. Extraction of the most intense band afforded cis azido O-TMS derived alcohol (-)-6.31.

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3-Azido-3-deoxy-4-O-(trimethylsilyl)-

-arabinal (-)-(6.31): R

= 0.86 (4:6 hexane/AcOEt); [α]

-198.0 (c 0.99, CHCl

).

H NMR (CDCl

) δ 6.44 (dd, 1H, J= 6.0, 0.8 Hz), 4.74 (dd, 1H, J= 6.0, 5.3 Hz), 4.08-4.17 (m, 1H), 3.85-3.92 (m, 1H), 3.83-3.84 (m, 1H), 3.80-3.82 (m, 1H), 0.19 (s, 9H).

C NMR (CDCl

) δ 147.3, 96.9, 67.8, 65.7, 56.2, 0.1.

Reaction of epoxide 6.1 with CbzNHNa (Protocol B)

Formation of benzyl carbamate sodium salt (Solution A). A solution of benzylcarbamate (0.200 g, 1.323 mmol, 3.0 equiv) in anhydrous THF (1.5 mL) was treated with 1M solution of NaHMDS (1.32 mL, 1.323 mmol, 3.0 equiv) at -78°C and the reaction mixture was stirred for 1 h at the same temperature.

Formation of epoxide 6.1 (Solution B). Following the previously described procedure, a solution of trans hydroxy mesylate 6.9 (0.080 g, 0.41 mmol) in anhydrous THF (4.0 mL) was treated with t- BuOK (0.050 g, 0.45 mmol, 1.2 equiv) and the reaction stirred until cyclization to epoxide 6.1 was achieved (TLC). After that, Solution A was added dropwise and the resulting reaction mixture was stirred overnight. Typical workup afforded a crude product (0.119 g) consisting of β-N-glycoside (+)-6.32, which was subjected to preparative TLC, using a 7:3 hexane/AcOEt mixture as the eluant.

Extraction of the most intense band afforded β-N-glycoside (+)-6.32 (0.019 g, 20% yield), pure as a colorless liquid.

N-(Benzyloxycarbonyl)-2,3-dideoxy-β-^L

-glycero-pent-2-enopyranosyl amine (+)-(6.32): R

= 0.28 (7:3 hexane/AcOEt); [α]

+3.7 (c 0.47, CHCl

);

H NMR (CDCl

) δ 7.29-7.39 (m, 5H), 5.99-6.07 (m, 1H), 5.80 (ddd, 1H, J = 10.3, 4.2, 1.8 Hz), 5.00-5.04 (m, 1H), 4.83 (d, 1H, J= 11.8 Hz), 4.58 (d, 1H, J = 11.8 Hz), 3.84 (ddd, 1H, J = 11.0, 5.5, 1.9 Hz), 3.75 (dd, 1H, J = 11.0, 8.4 Hz).

C NMR (CDCl

) δ 156.2, 137.9, 133.4, 128.7, 128.6, 128.4, 128.3, 127.9, 93.7, 70.2, 67.2.

Reaction of epoxide 6.1 with CbzNHNa (Protocol B)

Formation of benzyl carbamate sodium salt (Solution A). Following the previously described procedure, a solution of benzylcarbamate (0.035 g, 0.231 mmol, 3.0 equiv) in anhydrous THF (0.3 mL) was treated with 1M solution of NaHMDS (0.23 mL, 0.231 mmol, 3.0 equiv) at -78°C and the reaction mixture was stirred for 1 h at the same temperature.

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Formation of epoxide 1.1β (Solution B). Following the previously described procedure, a solution of trans hydroxy mesylate 1.3β (0.024 g, 0.077 mmol) in anhydrous THF (2.0 mL) was treated with t-BuOK (0.010 g, 0.092 mmol, 1.2 equiv) and the reaction stirred until cyclization to epoxide 1.1β was achieved (TLC). After that, Solution A was added dropwise and the resulting reaction mixture was stirred overnight. Typical workup afforded a crude product (0.056 g) consisting of β- N-glycoside (-)-6.33, which was subjected to preparative TLC, using a 1:1 hexane/AcOEt mixture as the eluant. Extraction of the most intense band afforded β-N-glycoside (-)-6.33 (0.019 g, 70%

yield) pure as a colorless liquid.

N-(Benzyloxycarbonyl)-[6-O-(benzyl)-2,3-dideoxy-β-^D

-threo-hex-2- enopyranosyl] amine (-)-6.33: R

= 0.48 (1:1 hexane/AcOEt); [α]

- 5.8 (c 2.85, CHCl

);

H NMR (CDCl

) δ 7.26-7.42 (m, 10H), 6.13 (ddd, 1H, J= 10.1, 5.0, 1.5 Hz), 5.87 (dd, 1H, J= 10.1, 1.0 Hz), 5.17 (d, 1H, J=

1.5 Hz), 4.92 (d, 1H, J= 11.8 Hz), 4.71 (d, 1H, J= 11.8 Hz), 4.67 (s, 2H), 3.91-3.99 (m, 1H), 3.69-3.90 (m, 3H).

C NMR δ 156.2, 138.3, 137.6, 136.4, 133.1, 131.3, 131.0, 130.4, 128.7, 128.6, 128.3, 128.2, 127.9, 127.2, 93.0, 74.6, 73.8, 70.3, 70.0, 67.2, 63.1.

Reactions of epoxides 6.1 with N-Nucleophiles (protocol A) Reaction of epoxide 6.1 with PrNH

A solution of trans hydroxy mesylate 6.9 (0.050 g, 0.257 mmol) in PrNH

(3.0 mL) was treated with t-BuOK (0.029 g, 0.308 mmol, 1.2 equiv) at room temperature and the reaction mixture was stirred 12 h. Dilution with Et

O and evaporation of the washed (brine) organic solution afforded a crude reaction product (0.051 g) consisting of trans 1,2-addition product (+)-6.26, which was subjected to preparative TLC, using a 9:1 CH

Cl

/MeOH as the eluant. Extraction of the most intense band afforded cis-1,2-N-propylamino alcohol (+)-6.26, pure as a liquid (0.016 g, 40%

yield).

3-N-Propylamino-3-deoxy-

-lyxal (+)-(6.26): R

= 0.21 (2:8 hexane/AcOEt);

[α]

+84.5 (c 1.65, CHCl

).

H NMR (CDCl

) δ 6.40 (dd, 1H, J = 6.1, 1.4 Hz), 4.78 (ddd, 1H, J = 6.1, 3.4, 0.6 Hz), 4.04 (dd, 1H, J = 10.4, 2.3 Hz), 3.85 (dd, 1H, J

= 6.7, 0.8 Hz), 3.77-3.81 (m, 1H), 3.75 (dd, 1H, J = 6.7, 2.3 Hz), 2.58 (dd, 2H, J = 7.8, 6.5 Hz), 1.53 (septet, 2H, J = 7.8 Hz), 0.92 (t, 3H, J = 7.8 Hz).

C NMR (CDCl

) δ 145.3, 100.1, 67.1, 66.9, 55.9, 48.7, 23.2, 11.9.

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