1,4-Chirality transfer via the ester enolate Claisen rearrangements in the preparation of (25R)- and (25S)-cholestenoic acids

Formation of the steroidal C-25 chiral center via the asymmetric alkylation methodology

A novel approach for the preparation of steroids containing a chiral center at C-25 is reported. The key stereochemistry inducing step was asymmetric alkylation of pseudoephenamine amides of steroidal C-26 acids. The reaction proceeded with high diastereoselectivity (dr > 99 : 1). The developed methodology was successfully applied to the synthesis of (25R)- and (25S)-cholestenoic acids as well as (25R)- and (25S)-26-hydroxy brassinolides.