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Aims and summary of the work.
This work has been aimed to the study of insoluble polymer-bound (IPB) chiral organocatalysts to be used under continuous flow or batch conditions for enantioselective transformations.
For the preparation of IPB chiral organocatalysts inside microreactors two different strategies were taken into consideration: (a) bottom-up approach, where proline derivatives were supported by means of copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) on methacrylic polymer brushes, grown by atom transfer radical polymerization (ATRP) on the inner walls of a microchip A; (b)
copolymerization of proline-bearing styrenic monomer with styrene and
divinylbenzene (DVB) to produce a resin monolith within an empty HPLC column B.
In the former approach the inner walls of the microchip were functionalised with a radical initiator and then poly(3-azidopropyl methacrylate) (PAzPMA) or poly(glycidyl methacrylate) (PGMA) polymer brushes were grown by ATRP. Proline derivatives bearing different protecting groups were then supported by CuAAC. Unfortunately all efforts to deprotect the chiral units failed, preventing the use of the device in catalytic runs.
In the latter approach, CuAAC was used to prepare styrenic monomers bearing protected proline units, which were then subjected to radical precipitation-polymerization with divinylbenzene, inside HPLC columns. After deprotection of the chiral moieties, the columns were used in the aldol addition of cyclohexanone to 4-nitrobenzaldehyde.
For the use in batch reactions we developed a novel pyrrolidine-sulfonamide organocatalyst supported by CuAAC on commercial Merrifield resin C.
The IPB catalyst was studied under batch conditions for the α-amination of iso-valeraldehyde with dibenzyl azodicarboxylate (DBAD), the aldol addition of
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cyclohexanone to 4-nitrobenzaldehyde and the addition of propionaldehyde to β-nitrostyrene.
