Base-catalyzed transhydrocyanation

In 1992, Oda et al. reported a one-pot synthesis of optically active cyanohydrin acetates from aldehydes, which were converted to the corresponding racemic cyanohydrins through transhydrocyanation with acetone cyanohydrin, catalyzed by a a strongly basic anion-exchange resin [46]. The racemic cyanohydrins were acetylated by a lipase from P. cepacia (Amano) with isopropenyl acetate as the acyl donor. The reversible nature of the base-catalyzed transhydrocyanation enabled continuous racemization of the unreacted cyanohydrins, thereby effecting a total conversion (Figure 4.21). 

Cyanohydrins are readily racemized with base, and this has been exploited by Oda and co-workers in a dynamic kinetic resolution of these substrates[10, n. In a typical procedure (Fig. 9-4), the cyanohydrins were formed by transhydrocyanation with acetone cyanohydrin, catalyzed by the hydroxide form of an anion exchange resin (Amberlite IRA-904). The reversible nature of the cyanohydrin formation allows racemization to proceed during the course of the enzyme-catalyzed acetylation, and the choice of isopropenyl acetate as the acyl donor means that the only by-product is acetone. 

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See also in sourсe #XX -- [ ]

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