Lewis acid catalyzed highly regio- and stereocontrolled trans- hydrosilylation of alkynes and allenes

Lewis acids such as AlCl₃ or EtAlCl₂ dramatically catalyzed the hydrosilylation of alkynes 1 with trialkylsilanes to produce the corresponding cis-vinylsilanes 2 in a regio- and trans-stereoselective manner. For example, the hydrosilylation of 1-dodecyne 1a with triethylsilane in the presence of 0.2 equiv of AlCl₃ gave cis-1-(triethylsilyl)-1-dodecene in 93% yield. Other alkyl- and phenyl-substituted terminal and internal acetylenes also underwent trans-hydrosilylation very smoothly. In the case of alkoxy- or silyloxy-substituted acetylenes, the use of 1.2 equiv of AlCl₃ or EtAlCl₂ was essential to obtain the corresponding trans-hydrosilylation products in high yields. Moreover, AlCl₃ catalyzed the hydrosilylation of aromatic allenes 11, producing the alkenylsilanes 12 with high regio- and stereoselectivities in moderate to high chemical yields. Not only the simple monosubstituted, but also the disubstituted and trisubstituted allenes, underwent the hydrosilylation reaction smoothly, serving as a useful tool for the synthesis of differently substituted vinylsilanes which are not easily available through the previously known methodologies. The mechanisms for these catalytic reactions of alkynes and allenes are proposed.