Radical Carbonylation of 1,5-Enynes Using TTMSS as a Chain Carrier. Unexpected Formation of Persistent 3-Silyl-1-siloxyallyl Radicals Serving as a Chain Breaking Path

The radical carbonylation of 1,5-enynes 1a and 1b using TTMSS as radical mediator gave the predicted carbonylative cyclization products 2a and 2b, respectively, in poor yields. The isolation and characterization of reaction byproducts by X-ray crystallographic analysis suggest that the poor chain propagation can be attributed to the formation of long-lived 3-silyl-1-siloxyallyl radicals, produced by the addition of a (TMS)3Si radical onto the O–C double bond of the initially formed cyclopentanones.