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), towa rd silyllithium reagents has been studied. Reactions of 1a-d with [tri s(trimethylsilyl)silyl]lithium gave the corresponding lithium silenola tes, (Me(3)Si)(2)Si = CROLi (5a, R = Mes; 5b, R = o-Tol; 5c, R = Ad; 5 d, 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 rea ctions under the conditions used. Acetylpolysilane 1h did not afford t he lithium silenolate but gave lithium [tris(trimethylsilyl)silyl]ethe nolate. Lithium silenolate 5a was produced also by treating 1a with (d imethylphenylsilyl)lithium. The re actions of 1b,c with (dimethylpheny lsilyl)lithium proceed in a different fashion from that of 1a to affor d products arising from addition of the silyllithium to the carbonyl b ond as major products. Lithium silenolates 5a,c,d are stable at low te mperature in THF solution and can be characterized by NMR spectroscopy . Silenolates 5a-d reacted with alkyl halides to afford Si-alkylated p roducts 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.