Thermal extrusion of silylenes from 1, 1-dimesitylsilacyclopropenes and 1,1-bis(2,6-dimethoxyphenyl)silacyclopropene was studied. Heating 1,1-dimesityl-2-(trimethylsilyl)-3-phenyl-1-silacyclopropene at 250degreesC led to the clean formation of dimesitylsilylene, which was readily trapped by methyldiphenylsilane, giving the insertion product. The rate of the silylene extrusion was affected by the substituents at the ring silicon and carbon atoms. Thus, replacement of the phenyl group on the carbon by a trimethylsilyl group, as well as substitution of the silicon by 2,6-dimethoxyphenyl groups in place of mesityls, clearly facilitate the silylene extrusion.