Stereoselective Synthesis of (E)-α-Selenenylvinylsilanes via the Hydromagnesiation Reaction of Alkynylsilanes

Abstract

E)-a-Selenenylvinylsilanes have been synthesized stereoselectively via the hydromagnesiation of alkynylsilanes, followed by the reaction with arylselenenyl bromides. (E)-aSelenenylvinylsilanes can undergo the desilylation reaction in the presence of a catalytic amount of hydriodic acid to give (E)-vinyl selenides in high yields.Bifunctional-group reagents, which have two different functional groups linked to the olefinic carbon atoms, for example, Sn-Si, Si-Zr, Se-B, Se-Sn, and Se-Zr combinations, play an important role in organic synthesis, especially in developing many convenient methods for the stereoselective preparation of substituted alkenes. These reagents and their synthetic applications have been reported. 1 Both vinylsilanes and vinyl selenides are important intermediates, but the bifunctional-group reagent containing selenium and silicon has rarely aroused attention. Recently, Xu et al. 2 described that alkynylsilanes underwent hydrozirconation and the successive reaction with selenenyl bromides to give (E)-a-selenenylvinylsilanes. Hydromagnesiation has emerged as a unique hydrometalation with some attractive features, such as the high regioselectivity and stereoselectivity observed with alkynylsilanes. 3,4 We now wish to report that (E)-aselenenylvinylsilanes could be synthesized by hydromagnesiation of alkynylsilanes, followed by treatment with selenenyl bromides.Alkynylsilanes 1 were prepared according to the literature procedure. 5 Hydromagnesiation of alkynylsilanes at 25 °C in diethyl ether for 6 hours gave (Z)-a-silylvinyl Grignard reagents 2, which reacted with selenenyl bromides 3 in THF to afford (E)-a-selenenylvinylsilanes 4. The yields were 68-86% (Scheme 1).