Asymmetric Wittig reactions of chiral arsonium ylides. Part 3: Reversal of stereochemistry caused by metal cation in enantioselective olefination of 4-substituted cyclohexanones using a C-2-symmetric chiral arsine

摘要

A novel C-2-symmetric chiral arsine was synthesized from (S)-(-)- 1, 1'-bi-2-naphthol in three steps. It was employed in the enantioselective olefination of 4-substituted cyclohexanones via a stabilized ylide formed in situ from the corresponding arsonium salt. Enantioselectivity up to 40% was obtained. Moreover, a reversal in the stereochemistry of the product was observed simply by changing the counter cation of the base from lithium to potassium. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 61]