Electrochemical synthesis of cyclic alkylsilanes

The electrochemical reduction of aliphatic α,ω-dibromides in the presence of polychlorosilanes of the formula RnSiCl4-n(n = 0, 2) was shown to afford heterocyclic silicon compounds in good yield (up to 91%). In contrast to non-electrochemical methods of synthesis of silacycloalkanes, based on the ring closure of terminal unsaturated compounds, the electrochemical route does not produce α-methylated byproducts and the heterocycle formation occurs quite selectively. The yield of cyclic organosilicon compounds goes through a maximum for 1,1-dimethyl-1-silacyclopentane (91%) and roughly decreases for 1,1-dimethyl-1-silacyclobutane (18%) and 1,1-dimethyl-1-silacycloheptane (57%). The formation of 5-silaspiro[4,4] nonane by the electrochemical process occurs with high selectivity despite the multitude of possible reaction pathways and the high probability of polymer formation due to the high functionality of the silicon. The relatively high selectivity of the electrochemical ring closure is suggested to be due to the orientating effect of an electrode in the course of an irreversible reduction of a CHal bond in the monosilylated intermediate. A possible mechanism for the process is discussed. © 1995