The S(H)i reaction at silicon - A new entry into cyclic alkoxysilanes

A new mild radical method for the preparation of cyclic five-membered alkox ysilanes is reported. This method comprises an intramolecular homolytic sub stitution reaction at silicon (S(H)i) Various leaving groups (SiMe3, GeMe3, SnMe3) were tested in the homolytic substitution reaction. We found that h igh yields were only obtained for silanes bearing a trimethylstannyl functi onality as leaving group in the S(H)i reaction. Rate constants for the cycl ization reaction were estimated by conducting standard competition experime nts. Based on the kinetic data, more elaborate reaction sequences such as r adical addition reactions with a subsequent S(H)i step were carried out. St ereoselective cyclization reactions were. also investigated. Excellent 1:2 diastereoselectivities were observed. The products of the SHi reaction, cyc lic alkoxysilanes, can easily be converted to the corresponding diol deriva tives by Tamao-Fleming oxidation as demonstrated for several examples.