An Unexpected Ring Contraction: Phenylsilane to Silacyclopentane

In the reaction of dimethoxymethylphenylsilane with Li in an excess of chlorotrimethylsilane, the phenyl group was readily reduced to give dimethoxymethyl(Ttc)silane (1; Ttc = 3,4,5,6-tetrakis(trimethylsilyl)cyclohexen-1-yl) in 45% yield. In addition, the diastereomeric isomers of 2-[2,2-bis(trimethylsilyl)ethylidene]-1-methoxy-1-methyl-3,4,5-tris(trimethylsilyl)silolane (2a,b) were also produced via an unexpected ring contraction in 20% and 8% yields, respectively. The structures of 2a,b were revealed by X-ray single-crystal crystallography.