Tetrahedron Letters No. 17, pp 1381 - 1384, 1976. Pcrgamon Press. Printed in Great Britain.
l?OLY-POD% LIGAITDS AS PHASE-TRA?JSFER CATALYSTS Roberto Fornasier and Fernando Icontanari"
Centro C.N.R. e Istituto di Chimica Industriale dell'Univcrsita*, Via C. Golgi 19, biilnno 20133, Italy.
Gianni Podda
Istituto di Chimica Organica, Facolta' di Parmacia, Via Ospedalc 72, Cagliari 09100, Italy.
Pietro Tundo
Istituto di Chimica Organica dell*Universita', Via Bidone 36, Torino 10125, Italy.
(Received in UK 1 -oh 1976; rcoeptcd for publication 15 March 1976) Several organic systems, such as onium salts,' crown ethers 2
, and aza- macrobicyclic polyethers, are capable of activating anions, by transfering 3 them from an aqueous or solid phase to an immiscible organic phase as a
poorly solvated and associated ion Pair. These therefore ma:? be used as phase- transfer catalysts in anion promoted reactions. It has been shocn' that "man:.' armed" acyclic polycthers operate as polypode li,yands nith alkaline andalkaline- earth cations, extracting them from water as picrates soluble in an organic medium. In the case of the benzene hexakis(2-this-5,8,11-trioxapentadecane) &
the extmctive effectiveness4 is similar to that of aza-macrobicyclic polyethers [221] and [2223 but, in contrast to the latter, l_i.is a very poor catalyst, at least in solid-liquid nhaoe-transfer rcactions.5
We have found that other polypode ligands show good phase-transfer catalytic activity. The systems examined belong to classes g,i,&,_$, and g,2,5aT$.,deriwd from 1,3,5-triazine and pentaerythritol, respectively. Compounds a,$+.more
prepared by condensation of p-trichlorotriazine aith bis (3,6,9,12-tetraoxa- hexadecyl) and bis (3,6,3,12-tetraoxaeicosyl)amine 6 (b enzene, Xt R;
3 2h at 2!T"-450, followed by 12h at 800); amI compound s ,?z,z by condensation of trichlorotriazine with monobutyl ,and monooctgl triethylene&co17 (toluene, t-BuOK; 2h at 25*-45O, fOllOTJed by 12h at l:O"). Compound $a_ was obtained by condensation of mono-n-decylpentaer:.'thritol \?ith ClCH2COOH, reduction with LiAlH4 and subsequent repetition of the two reactions. Compound 2 was prepared from 4a by the same sequence of reactions. Alkylation of 4a and
lY31
1x32 m. 17
with n-octyl bromide afforded ethers 2 and 2, respectively.
a
CH OAOAOR' 2
(n-C4HgOnOAOnO~)2N 2 R = n-C4H90nOnOnO-
(n-C#,7O nCIAOAOq)N 3b R=nCH
2 M -
a
17 OnOnOmO-% R'=H 2 R ' = PC~H,~
% R' = CH2CH20H ZR ’ = n-CaH,70CH2CH2-
Some examples of catalgtic activity of compounds 2-2 in phase-transfer reactions are reported in the Table. In the triazine series the activity is maximum for COUI_pOUnd,~& with six polyoqrethylene branches, and diminishes when the terminal alkyl group is shortened (2) or the number of branches is reduced to three (2, 2). The efficiency of 2 is similar to that of a typical phase- transfer catalyst, hexadecyl tributyl phosphonium bromide 2, and close to that3 of the alkyl-substituted aza-macrobicyclic polycthers, which probably represent the best type of catalyst.
In the case of 2 the catalytic activity is high for all the reactions examined, but for other compounds it is noticeably dependent on the reaction.
This fact is particularly true for the pentaerythritol derivatives: compounds 5 are fairly efficient in the nucleophilic substitution of bromide with I- &i PhS- in I-bromooctane and in the reduction of ketones to alcohols with BH;, but they are completely inactive in the formation (ana alkylation) of carbanions.
Catalysts Ja,b_are ineffective not only in the formation of carbanions, but also in Br/I exchange, although they show some activity in the formation of thioethers and in the reduction of ketones. Compounds _2a,Land 3,a,k are very good catalysts in the oxidation of alkenes with aqueous KMnO 4 (quantitative conversion of
l-octane to heptanoic acid in 30-60 min. at 250).
Insertion of aliphatic chains provides a degree of orgsnophilic character to compounds&A. It is possible that in some cases (see 2 and 2) associative apolar interactions among the terminal alkyl groups lead to a relatively stable cavity inside the polyoxymethylene chains and favour, therefore, the chelation of the metallic cation. A similar effect may be caused by intramolecular hydrog bonds among the terminal OH in 42 and 2. These effects should balance in part the unfavourabLe role that enthalphg and entropy factors (especially the latter play in polypoae systems, 9.
In comparison with multidentate polgcyclic li@nas such as [222] crgptatss.
en
1
lo. 17
Table
Substrate a Reagent Catalyst f
T/Y Time/h Yield$ g Proauct h
n-C8ff17Br 60
60 60 60 60 60 80 80 60 80 80 20
20 20 20 20 20 20 20 20 20 20 20 20 20 20
72 82
3 a5
3 45
2: (72) :: (86) 24 (72) 51 (87)
10 cl
10 <1
3 72
5 48
5 100
5 70
5 44
5 80
5 30
0.15 100
4 78
4 50
4 4
4 65
3 97
3 25
: 42 18 3 (9) 35 (60)
n'C8ff171
n-Ca’11,1 PPh
a The reactions were carried out with a saturated aqueous solution of the reagent; no solvent b7a.8 sea for the substrate, except fo
borohydride red$ction. E
5 Mol. e uiv.
B '1 Mol. equiv.
5 benzene in the 1.2 Idol. equiv. in 505 aq. 9aOH. 1.5 Fdol. iquiv. 0.01 I,iol_. equiv. g By g.1.c. analysis.
h The prodycts were characterized by g.1.c. retention time and by comparison (i.r. aa H n.a.r. spectra) with authentic samples.
1384 No. 17
Rejerences and Notes
C.& Starks, J. Amer. Chen. Sot., 1971, 23, 195; J. Dockx, Synthesis, 1973, 441; E.V. Dehmlow, Angew. Chem. Intern. Zdn., 1974, lj, 170.
D. Landini, F. p'iontanari, and F.I. Pirisi, J.C.S. Chem. Comm., 1974, 879;
D. Landini, A.& Haia, F. Uontanari, and F.M. Pirisi, Gazzetta, 1975, II 863; Ii. Nakosza and M. Ludwikow, Angew. Chem. Internat. Edn., 1974, 12, 665;
F.L. Cook, C.W. Bowers, and C.L. Liotta, J. Orp. Chem., 1974, 2, 3416, and references therein; J.W. Zubrick, B.I. Dunbar, and H.D. Durst, Tetrahedron Lett., 1975, 71, end references therein.
B, Dietrich and J.N. I&n, Tetrahedron Lett., 1973, 1225; M. ulnquini, F.
?Jontanari, and P. Tundo, J.C.S. Chem. Comm., 1975, 394.
F. V&$le and E. Weber, Angew. Chem. Internat. Edn., 1974, 1.3, 814.
A. Knb;chel, J. Ochler, and G. Rudolph, Tetrahedron Lett., 1975, 3167.
From N-tritylditosyldiethanolsmine, triethyleneglycol monoalkyl ether ana t-BuOK in DMSO for 48h at loo*,
far 30 min. at r.t.
and successive detritylation with HCl-H20-t$eOH
From triethyleneglycol monotetrahydropyranyl ether, n-alkyl bromide =a t-BuOK in anhydrous THY for 12h at reflux,
ma
successive,depyranylation with HCl-H20-MeOH for 30 min. at r.t.compounds A-2 are v';scous oils , purified by column chromatography. Elemental analyses, i.r. and H n.m.r. data are in agreement with the assigned structW=$
J.P. ~ehn, Structure
