Silicon-carbon unsaturated compounds .55. Synthesis and reactions of lithium silenolates, silicon analogs of lithium enolates

Chemical behavior of acylpolysilanes, (Me(3)Si)(3)SiCOR (1a, R = Mes; 1b, R = o-Tol; 1c, R = Ad; 1d, R = t-Bu; 1g, R = Ph; 1h, R = Me), toward silyllithium reagents has been studied. Reactions of 1a-d with [tris(trimethylsilyl)silyl]lithium gave the corresponding lithium silenolates, (Me(3)Si)(2)Si = CROLi (5a, R = Mes; 5b, R = o-Tol; 5c, R = Ad; 5d, R = t-Bu), in high yield by removal of a trimethylsilyl group from the acylpolysilane. However, a similar reaction of 1g gave an unstable lithium silenolate, which undergoes dimerization and then further reactions under the conditions used. Acetylpolysilane 1h did not afford the lithium silenolate but gave lithium [tris(trimethylsilyl)silyl]ethenolate. Lithium silenolate 5a was produced also by treating 1a with (dimethylphenylsilyl)lithium. The re actions of 1b,c with (dimethylphenylsilyl)lithium proceed in a different fashion from that of 1a to afford products arising from addition of the silyllithium to the carbonyl bond as major products. Lithium silenolates 5a,c,d are stable at low temperature in THF solution and can be characterized by NMR spectroscopy. Silenolates 5a-d reacted with alkyl halides to afford Si-alkylated products in high yield. Treatment of 5a,b with chlorotriethylsilane led to the formation of silenes arising from O-silylation of the lithium silenolates, almost quantitatively, while 5c,d gave the corresponding acylpolysilanes by Si-silylation in high yield. Results of theoretical studies which were carried out using the reaction of (H3Si)(3)SiCOCH3 with H3SiLi as a model also are described.