Lactones 23: Synthesis of cis-fused bicyclic hydroxy lactones with a p-menthane system
摘要:
Enantiomeric pairs of cis-fused bicyclic hydroxy lactones with a p-menthane system were obtained in a several step synthesis from enantiornerically pure isomers of (+)-(R)- and (-)-(S)-pulegone. One-pot allyl-Claisen rearrangement of cis-pulegols, epoxidation of gamma,delta-unsaturated p-nitrophenyl esters and acidic lactonization of epoxy esters are key synthetic steps. The structures of the compounds were confirmed by both spectroscopic and crystallographic methods. (c) 2005 Elsevier Ltd. All rights reserved.
from α-substituted (homo)allyl alcohols. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl esters and carbonates or vinyloxiranes. [¹] cyclopropanation - Barbier conditions - Grignard addition - alkyllithiumaddition - dibromomethane
Starting from (R)-(+)- and (S)-(−)-pulegone enantiomeric pairs of hydroxy lactones and keto lactones were obtained by Claisen rearrangement of cis-pulegols and lactonization of epoxy esters. The hydroxy lactones were reduced with LiAlH4 in order to assign the configuration of the chiral centers. The structures of the synthesized compounds were established on the basis of spectroscopic and crystallographic