PD-CATALYZED COUPLING REACTION OF ACETYLENES, IODOTRIMETHYLSILANE, AND ORGANOZINC REAGENTS FOR THE STEREOSELECTIVE SYNTHESIS OF VINYLSILANES

The reaction of terminal acetylenes with Me(3)SiI (1) and organozinc reagents in the presence of Pd(PPh(3))(4) results in addition of the trimethylsilyl group of 1 and an alkyl group of the organozinc reagent to the acetylenes. In all cases the trimethylsilyl group adds to the terminal carbon of the acetylenes. Both aromatic and aliphatic terminal acetylenes undergo the coupling reaction with high regio- and stereoselectivities. The yield and stereoselectivity are relatively sensitive to the nature of the organozinc reagent used. The reaction of phenylacetylene (2) using Bu(2)Zn gives the corresponding coupling product in high yield with high stereoselectivity (>98%). In contrast, the use of BuZnI results in 92% stereoselectivity. The stereoselectivity for the reaction using (Me(3)-SiCH2)(2)Zn is lower than those for Me(2)Zn, Et(2)Zn, and Bu(2)Zn. For organozinc reagents, alkylzinc works well while phenyl-, ethynyl-, and allylzinc do not. The reaction using Me(3)SiCl, Me(3)SiBr, Me(3)SiSPh, Me(3)SiSePh, and Me(3)SiOTf in place of 1 does not proceed. The reaction with Me(3)SiMe(2)-SiI and Me(3)SiMe(2)SiMe(2)SiI in place of 1 gives the corresponding vinyldisilane and -trisilane, respectively.