Unusual Tandem Alkynylation and trans-Hydrosilylation To Form Oxasilacyclopentenes

[reaction: see text] An unusual tandem reaction sequence to form oxasilacyclopentenes from carbonyls and alkynylsilanes in the presence of a catalytic amount of nucleophilic initiator has been discovered. The reaction proceeds readily at room temperature and is applicable to a wide variety of carbonyl substrates. While the reaction scope tolerates variable substitutions on the alkynylsilane, phenylacetylene-derived silane variants consistently achieved the best yield.