Organocopper(I) mediated synthesis of 1-alkenylsilanes and 1,3-alkadienylsilanes from ethynylsilanes

Abstract

Ethynylsilanes (I) are converted into α-silyl substituted (Z)-alkenylcopper(I) compounds (II) by treatment with RCu reagents. The adducts II react with a variety of electrophiles to give the 1-alkenylsilanes RCH=C(E)SiR3′ (III: E = H, Cl, Br, I, CN, SnMe3, SMe, Me, H2CHCH2). The conversion of I into III (E = H) can also be effected by using homocuprates, R2CuMgCl, and triorganodicuprates, R3Cu2MgCl. The latter reagent should be used when the group R is methyl. An interesting 1,3-diene formation is observed on treating excess of ethynyltrimethylsilane (Ib) with R3Cu2MgCl; this reaction involves addition of intermediary vinylcuprates to unreacted 1-alkynylsilane (Ib). The intermediary 1,3-dienyl adduct (VIIb) reacts with various electrophiles to give 1,3-dienes, RCH=C(SiMe3)CH=C(E)SiMe3 (VIIIb).