Thomas F. O. Lim

Regioselective hydroborations of methylvinylchlorosilanes

Abstract The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl n Me3− n SiCH CH2 ( n = 0 − 3), has been investigated using BH3←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols for n = 0 and 1. For n = 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol- 0 - d provides a more effective means of derivatization. Addition of the alkenes, n = 2 or 3, to excess BH3←THF gives ca . 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes give ca . 80% of the β-boron adducts.

The methoxide promoted protonolysis of organosilylboranes

Abstract The destructive distillation or pyrolysis of borane 9-borabicyclo[3.3.1]nonane, or dicyclohexylborane adducts to vinylsilanes which have been treated with sodium methoxide in methanol gives significant yields of products resulting from protonolysis of the CB bond. Both α- and β-boro adducts undergo the reaction, which is favored when silicon has methoxy substituents. Quantitative incorporation of deuterium in the saturated products when methanol-O-d is used as the solvent shows that the hydroxyl group of methanol is the proton source. The absence of isomerization of the alkyl groups attached to silicon in the protonolysis of the adducts to propenyltrichlorosilane or isopropenyltrichlorosilane indicates that cyclic intermediates or free carbanions are not involved in the reaction.

THE WITTIG SYNTHESIS OF ALLYLIC ORGANOSILICON COMPOUNDS

Abstract : The reactions of Beta-silylalkylidenetriphenylphosphoranes, prepared by the action of alkylidenetriphenylphosphoranes on iodomethyl-silicon compounds, followed by deprotonation of the resulting Beta-silylalkyltriphenylphosphonium iodides, with aldehydes and ketones provide a useful route to allylic silicon compounds.

THE SYNTHESIS OF 3,3-DIFLUOROALLYL DERIVATIVES OF SILICON BY AN ORGANOPHOSPHORUS ROUTE

Abstract : 3,3-Difluoroallylderivatives of silicon have been prepared by the reaction of difluorochloromethane with ylides of type Ph3P=CHCH2SiR3 (SiR3 = SiMe3, SiMe2H, SiMe2OSiMe3, SiMe(OSiMe3). Also prepared by this procedure was Me3SiCH2C-2 (CH3)=CF2, but Me3SiCH2c(C6H5)=CF2 could not be prepared in this way, probably because the ylide, Ph3P=C(C6H5) CH2SiMe3 was not sufficiently basic to deprotonate HCF2C1. The thermal stability of Me3SiCH2CH=CF2 was assessed and a few of its reactions examined: additon of CCl2 and CBr2 (generated via the appropriate PhHgCX2Br) and addition-elimination reactions with phenyl- and n-butyllithium to give Me3SiCH2CH=C(R)F (R = Ph, sub bar n-Bu). (Author)