Generation of the 1,3-Phosphasilolene Skeleton from Ortho-Silylated Biarylphosphonates

Treatment of diethyl 2-(3-trimethylsilyl)biphenylphosphonate 15 with excess methyllithium affords a mixture of the 2H-benzo[d]-1,3-phosphasilolen-1-one 16 together with the silyl transfer product 17. Deuterium incorporation studies show that the mechanism involves the conversion from 15 to 19 and 20, followed by formation of a siliconate intermediate 21. Cleavage of an exocyclic Si-C bond affords 16 while endocyclic C-Si cleavage leads to 17. The phosphasilolene structure 16 is confirmed by X-ray crystallography.