A new synthesis of allenic hydrocarbons from tertiary 2‐propynyl sulfinates and organocopper(I) compounds. Evidence for a <i>syn</i>‐l,3‐substitution pattern in the steroid series

Abstract

Abstract In tetrahydrofuran tertiary 2‐propynyl sulfinates R 1 ‐C≡C‐C(R 2 ,R 3 )‐OS(O)Me (1) are smoothly converted in a 1,3‐substitution reaction into allenic hydrocarbons RR 1 CCCR 2 R 3 (4) by organoheterocuprates of the type (RCuBr)MgX. Generally, much attack on the sulfur atom in 1 is observed when this compound is treated with (RCuBr)MgX in diethyl ether, or with R 2 CuMgX in diethyl ether or in tetrahydrofuran. The stereochemical course of the allene formation has been studied in the case of the sulfinic ester 5, derived from the steroid “Mestranol”. It is found that the syn ‐1,3‐substitution product 6 is exclusively formed from 5 and the heterocuprates (MeCuBr)MgCl or (MeCuBr)MgCl·LiBr. Most likely, copper(III) species are formed in the first step of the 1,3‐substitution reactions described.