Oxyketene imines

Scheme 19 Catalytic, enantioselective additions of Af-silyl oxyketene imines...

An interesting extension of this method involves the reaction of Af-silyl oxyketene imines derived from cyanohydrins (Scheme 19) [81]. By judicious selection of the protecting group on the oxygen, highly functionalized (3-hydroxy cyanohydrins can be accessed with high levels of enantio- and diastereoselectivity. These products can then be transformed into a diversity of structural motifs (amines, aldehydes, imines, ketones) important for the synthesis of polyketide and other classes of natural products. In addition, the ethers can be easily converted to enantiomerically enriched unsymmetrical benzoins, thus revealing the synthetic equivalency of A-silyl oxyketene imines as acyl anions (Scheme 19). 

Denmark SE, Wilson TW (2010) A-silyl oxyketene imines are underused yet highly versatile reagents for catalytic asymmetric synthesis. Nat Chem 2 937-943... 

Furthermore, N-silyl oxyketene imines derived from protected cyanohydrins were found to serve as acyl anion equivalents in a similar reaction manifold, enabling the efficient preparation of cross-benzoin and glycolate-aldol products in an almost stereochemically pure form (Scheme 7.11) [18]. 

Scheme 7.11 Addition of N-siiyi oxyketene imines cataiyzed by 2.

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