Formation and Reactivity of Silacyclopropenes Derived from Siloxyalkynes: Stereoselective Formation of 1,2,4-Triols

Silver phosphate-catalyzed silylene transfer to siloxyalkynes provided silacyclopropenes possessing a silyl enol ether functional group. Copper-catalyzed insertions of carbonyl compounds afforded the corresponding oxasilacyclopentenes. The embedded silyl enol ether functionality was treated with various aldehydes and a catalytic amount of Sc(OTf)3 to provide dioxasilacycloheptanones, which resulted from an aldol addition/rearrangement. Stereoselective reduction or allylation of the cyclic ketone, followed by n-Bu4NF deprotection, provided high yields of 1,2,4-triols possessing four contiguous stereocenters.