Insertion into carbon-hydrogen bonds is a well-known reaction in the chemistry of carbenes [l]. Seyferth and coworkers have found that dichloro- carbene, generated by pyrolysis of phenyl(bromodichloromethyl)mercury, selectively inserts into SCH bonds of alkylsilanes, and proposed a fl-activ- ating effect of the silicon atom on the CH insertion [2]. However, Gaspar and coworkers [ 31 recently have reported that the silicon atom activates eCH bonds of ...