The reaction of phenyl(bromodichloromethyl)mercury with 1,1 -dimethyl-1 -silacyclobutane in benzene at 80°g ave the ring expansion product, 1,1 -dimethyl-2,2-dichloro-l -silacyclopentane, in 58% yield, as well as the ß C-H insertion product, 1,1 -dimethyl-3-dichloromethyl-l-silacyclobutane, in 12% yield. With 1,1,3-trimethyl-1-silacyclobutane analogous products were formed, but the C-H insertion product was favored by a small margin, the yields of 1,1,4-trimethyl-2,2-dichloro-l -silacyclopentane and 1,1,3-trimethyl-3-dichloromethylsilacyclobutane being 23 and 39%, respectively. In the case of 1-methyl-1-silacyclobutane the Si-H bond was much more reactive, giving 1 -methyl-1 -dichloromethyl-1 -silacyclobutane, but the latter also reacted with the mercury reagent to give 1 -methyl-1 -dichloromethyl-2,2-dichloro-l -silacyclopentane. 1,1,3,3-Tetramethyl-l ,3-disilacyclobutane was very unreactive toward PhHgCCl2Br, but under special conditions (no solvent, higher temperature) it did react to give 2,2dichloro-l,l,4,4-tetramethyl-l,4-disilacyclopentane in good yield. A complicating factor was the facile ß elimination of Si-Cl of the latter, to give 2,5-dichloro-3,3,5-trimethyl-3,5-disila-l-hexene.
