Synthesis of α-silylmethyl-α,β-unsaturated imines by the rhodium-catalyzed silylimination of primary-alkyl-substituted terminal alkynes.

In contrast to our previous report on the rhodium-catalyzed reaction of terminal alkynes with equimolar amounts of hydrosilanes and isocyanides leading to (E)- or (Z)-β-silyl-α,β-unsaturated imines A, the addition of an excess molar amount of hydrosilanes relative to isocyanides in the reaction of primary-alkyl-substituted terminal alkynes results in the production of α-silylmethyl-α,β-unsaturated imines B. Various isocyanides bearing tert-butyl and 1-adamantyl groups gave B with good product selectivity. Z isomers were formed stereoselectively in many cases. Regarding the mechanism for this reaction, when the hydrosilane was added to the reaction mixture in two portions, unsaturated imines A were initially formed, which then underwent double-bond isomerization, probably catalyzed by a Rh-H species, to give B.