1,1,3,3-Tetrakis(alkylthio)-1,3-dilithio-2-silapropanes: Useful reagents for the synthesis of polysilacycloalkanes via dianionic ring formation

Treatment of 1,1,3,3-tetrakis(alkylthio)-2-silapropanes with t-BuLi in THF at -40 °C generated 1,1,3,3-tetrakis(alkylthio)-1,3-dilithio-2-silapropanes which reacted with various bifunctional chlorosilanes to give the corresponding 4-to 7-membered polysilacycloalkanes in moderate to good yields.Furthermore, double alkylation of the dilithiated silanes with bis(halomethyl)diorganosilanes or dihaloalkanes was found to proceed smoothly giving rise to 1,4-disilacyclohexanes or silacycloalkanes in good yields, respectively, in THF and an aprotic polar co-solvent such as hexamethylphosphoric triamide (HMPA) or 1,1,3,3-tetramethylurea (TMU).The sulfenyl groups in the cyclized products were smoothly removed by radical reduction with tributyltin hydride.