Unexpected metal base-dependent inversion of the enantioselectivity in the asymmetric synthesis of alpha-amino acids using phase-transfer catalysts derived from cinchonidine

摘要

dNew cinchonidinium salts bearing a 3,5-dialkoxybenzyl group show an alkaline metal base-dependent reversal of enantioselectivity when used as phase-transfer catalysts in the asymmetric alkylation of N-(diphenylmethylene)glycine isopropyl ester with benzyl bromide. The use of potassium hydroxide as base in this alkylation reaction afforded the (S)-enantiomer, whereas using sodium hydroxide under the same conditions afforded the corresponding (R)-enantiomer. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 60]