Chiral Quaternary Ammonium Salts as Catalysts for the Strecker Reaction

Chiral Quaternary Ammonium Salts as Catalysts for the Strecker Reaction 

Using a-unbranched aldimines for the asymmetric Strecker reaction under PTC, somewhat lower ee s and yields were obtained than with branched analogues. These results can be ascribed to the partial imine hydrolysis and uncatalyzed cyanation of primary and secondary aldimines under PTC [44]. Therefore, N-arylsulfonyl a-amido sulfones 78 were employed for in situ generation of the imines species (Table 30.9). With catalyst 76, generally higher yields and higher enantioselectivities were obtained for various primary and secondary aliphatic N-arylsulfonyl a-amido sulfones 78. 

Erase and coworkers finally accompUshed transformation of the aromatic counterparts of 84 into the a-amino nitriles 86, by using the naturally occurring alkaloid quinine 85 (Table 30.10) [46]. Solid KCN led to liberation of the free N-carbamoyl imine by deprotonation of the a-amido suUbne 84 and subsequent elimination of the sulfinate. The so-generated HCN could subsequently protonate the catalyst 85 

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