Silylene-Mediated Polarity Reversal of Dienoates: Additions of Dienoates to Aldehydes at the δ-Position To Form trans-Dioxasilacyclononenes

Silylene transfer to α,β,γ,δ-unsaturated carbonyl compounds produced oxasilacyclopentenes that underwent thermal additions to aldehydes to produce trans-dioxasilacyclononenes as single stereoisomers. This reaction, which converts the δ-position of the unsaturated carbonyl compound into a nucleophilic center, represents an inversion of polarity from the normal pattern of reactivity. The stereospecificity of the reaction suggests that the addition to aldehydes occurred through a closed, chairlike six-membered transition state. This reaction can be used to prepare enantiomerically pure materials by the use of chiral auxiliaries to control the formation of the oxasilacyclopentenes. Functionalization of the resulting trans-cycloalkene occurred with complete stereoselectively.