THE PREPARATION AND ANALYSIS OF THE PHENYLDIMETHYLSILYLLITHIUM REAGENT AND ITS REACTION WITH SILYL ENOL ETHERS

Phenyldimethylsilyllithium is formed from lithium and phenyldimethylsi lyl chloride by slow cleavage of the Si-Si bond of 1,1,2,2-tetramethyl -1,2-diphenyldisilane after the rapid formation of the disilane. 1,1,2 ,2-Tetramethyl-1,2-diphenyldisiloxane, produced from the silyl chlorid e by reaction with oxides and hydroxides on the lithium metal surface, is cleaved by dimethyl(phenyl)silyllithium to give lithium dimethyl(p henyl)silanoxide. Dimethyl(phenyl)silyllithium reacts with 1,2-dibromo ethane to give dimethyl(phenyl)silyl bromide, which is so rapidly cons umed by excess silyllithium reagent that it does not interfere with th e double titration used to measure its concentration. Dimethyl(phenyl) silane, produced by protonation of the silyllithium reagent, is also c onsumed by the silyllithium reagent to give 1,1,2,2-tetramethyl-1,2-di phenyldisilane which regenerates the silyllithium reagent, as long as lithium is still present. By-products in the preparation of dimethyl(p henyl)silyllithium include 1,3-diphenyl-1,1,2,2,3,3-hexamethyltrisilan e dimethyldiphenylsilane and 1,4-bis[dimethyl(phenyl)silyl]benzene. Di methyl(phenyl)silyllithium displaces the silyl group from the tert-but yldimethylsilyl enol ether of cyclohexanone to give the lithium enolat e under relatively mild conditions.