Efficient Generation and Synthetic Applications of Alkyl-Substituted Siloxycarbenes: Suppression of Norrish-Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer.

Acylsilanes have been known to undergo isomerization to siloxycarbenes under photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrish-type fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study, generation of siloxycarbenes from alkanoylsilanes by visible-light-induced energy transfer was examined by using an Ir complex, [Ir{dF(CF3 )ppy}2 (dtbpy)]PF6 , and was successfully applied to the C-C coupling reactions with boronic esters or aldehydes. This methodology efficiently suppressed undesired Norrish-type reactions and broadened synthetic utility of alkanoylsilanes.