Addition of a stable dialkylsilylene to carbon–carbon unsaturated bonds

The reactions of an isolable dialkylsilylene, 2,2,5,5‐tetrakis(trimethylsilyl)silacyclopentan‐1,1‐diyl ( 1 ) with ethylene, (Z)‐2‐butene, acetylene, bis(trimethylsilyl)acetylene, and 2,3‐dimethylbutadiene at room temperature gave the corresponding silacycles as isolable compounds. Because of the large steric hindrance, the reaction of 1 with (E)‐2‐butene gave a complex mixture, indicating no formation of the corresponding silirane. The reaction of 1 with 2,3‐dimethylbutadiene afforded the corresponding [1 + 4] cycloadduct without contamination of the [1 + 2] cycloadduct. Stable C‐unsubstituted silirane and silirene produced by the reactions of 1 with ethylene and acetylene were analyzed by X‐ray crystallography.