Synthesis of Silirenes by Palladium-Catalyzed Transfer of Silylene from Siliranes to Alkynes

Palladium-catalyzed reactions of cis -1,1-di- tert -butyl-2,3-dimethylsilirane with disubstituted alkynes produced thermally stable silirenes in high yields (81−86%). Alkyl-, aryl-, trimethylsilyl-, and heteroatom-substituted alkynes were employed. The silirenes reacted with phenylacetylene and <3 mol % of PdCl 2 (PPh 3 ) 2 to produce trisubstituted siloles. A common catalytic cycle involving palladasilacyclobutene accounts for both the formation of silirene and the trisubstituted silole. The palladium-catalyzed extrusion of silylene effectively transfers silylene from one strained ring (a silirane) to form another strained ring (a silirene) and represents an unusual metal-mediated process.