Réduction par les ions chromeux de derives bromopropargyliques en composés alléniques. application à la synthese de la phéromone de la bruche du haricot sec

Abstract

The racemic title compound 2(E) is obtained (77%) by reduction with chromous ions (THF+HMPT solvent, with anhydrous AcOH) of 7(E) readily prepared from 4 or propargylic diethylacetal as starting materials. In the reduction of 7(E) or 7(Z) with Cr 2+, the nature and ratios of the compounds obtained ( 2(E), 2(Z). 8(E), 9(E + Z), 10(E)) are strongly dependent on solvent (THF, or THF + HMPT) and on the protonation reagent (H 2O or AcOH). These results, and an IR analysis of the organochromium species generated from 7(E) or 7(Z) (A, B and C in equilibrium), suggest two mechanisms of protonolysis of the organochromium intermediates; mainly S E2 (THF+HMPT, anhydrous AcOH) or mainly S Ei' (THF, HsO). Some unsuccessful attempts at asymmetric induction in this reaction are reported.