Synthesis of natural γ-lactones and a dilactone pyrrolizidine alkaloid via the reactions of 2-propenyl-1,3-dithiane
Journal
Pure and Applied Chemistry
Journal Volume
68
Journal Issue
3
Pages
581-584
Date Issued
1996
Author(s)
Abstract
The crotyllithium generated from 2-propenyl-1,3-dithiane reacts exclusively at the γ-carbon with many aldehydes to give the homoallylic alcohols having the anti configuration. Hydrolyses of the addition products yield β,γdisubstituted γ-lactones such as whiskey lactone and an insect pheromone eldanolide. The homoallylic alcohols are resolved by catalysis with lipases and the method is applicable to syntheses of optically active γ-lactones. The addition reaction of the dithio-substituted crotyllithium and ethyl pyruvate in the presence of zinc chloride gave, however, the syn product. The product is regioselectively elaborated to an 11-membered dilactone pyrrolizidine alkaloid, crobarbatine, by esterification of retronecine at the allylic hydroxyl group and macrocyclization subsequently to hydrolysis of the ketenedithioacetal moiety. Regioselective reactions of the crotyllithium with acetals, orthoesters, aliphatic aldimines and three- to six-membered cyclic ethers are carried out by mediation of boron trifluoride.
Type
journal article