Silacarbocycles from ring expansion

Ring enlargement of silicon heterocycles is accomplished from derivatives which contain an exocyclic chloromethyl substituent by reaction with aluminum halide catalyst or with potassium fluoride. Tricyclic derivatives with a silicon atom in a central five-, six-, or seven-membered ring form silins, silepins and silocins, respectively, and are isolated by quenching the product chlorosilanes with H₂O, MeOH, Na/MeOH, LiAlH₄, MeMgBr or MeLi. A stoichiometric quantity of fluoride ion also results in conversion of 9-chloromethyl-9-silaanthracene to 5-fluoro-dibenzob,e] silepin but the percent conversion of the 9-iodomethyl precursor is higher. The limitations of the two methods are discussed briefly.