Robert F. Cunico

Generation of 1,2-dehydrobenzene from the dehalosilylation of (o-halophenyl)trimethylsilanes

Abstract ( o -Halophenyl)trimethylsilanes afford products expected from the generation of 1,2-dehydrobenzene when treated with potassium tert-butoxide or tetramethylammonium fluoride in aprotic solvents such as hexamethylphosphoric triamide and diglyme. The dehalosilylation leading to 1,2-dehydrobenzene appears to proceed by a stepwise process which involves the initial formation of an o -halophenyl carbanion resulting from heterolytic cleavage of the aryl—silicon bond.

geminal-dehalosilylation of α-halo-β,β-dimethylvinyltrimethylsilanes: generation of isopropylidene carbene

Abstract Treatment of α-chloro- or α-bromo-β,β-dimethylvinyltrimethylsilane with anhydrous tetramethylammonium fluoride (TMAF) in diglyme containing olefins led to isopropylidenecyclopropanes. A stepwise geminal dehalosilylation leading to isopropylidene carbene appears to be involved. The carbene is a species of low electrophilicity (ϱ0.41) and reacts stereospecifically with 2-butene. The substrates α-chloro-β,β-diphenylvinyltrimethylsilane, E -1-chloro-1-trimethylsilypropene and α-chlorovinyltrimethylsilane afford only acetylenes when treated with TMAF.

On the Preparation of Carbamoylsilanes

Abstract Various N,N-disubstituted carbamoyltrimethylsilanes can be prepared by the addition of LDA to a mixture of TMSCl and the appropriate formamide in THF at −78°C. Slow (syringe pump) addition of LDA is crucial to obtaining good yields.

Metalation of vinyltrimethylsilanes

Abstract Metalation of vinyltrimethylsilane and both trans-(VIII) and cis-(IX) 1-(trimethylsilyl)-3,3-dimethyl-1-butene with organolithium/TMEDA complexes was explored. Vinyltrimethylsilane underwent exclusive addition of tert-butyllithium to the double bond. Metalation of (VIII) occurred only at the trimethylsilyl function, while (IX) afforded both α-silylvinyl and trimethylsilyl position metalation.

The silapinacol rearrangement: Conversion of α,β-dihydroxysilanes into α-silyl carbonyl compounds

Abstract Treatment of α,β-dihydroxysilanes with trifluoroacetic acid in chloroform results in a 1,2-migration of the silyl group to give α-silyl aldehydes and ketones. The t -butyldimethylsilyl compounds can be isolated in high yields.

Generation of a vinylidene carbene from an α-chlorovinylsilane

Abstract The reaction of 1-chloro-1-trimethylsilyl-2-methylpropene with anhydrous tetramethylammonium fluoride in the presence of carbenophiles affords dimethylvinylidene insertion products.

Carbamoylsilanes from the in situ metalation–silylation of a formamide

Abstract In situ treatment (−78°C) of N-methoxymethyl–N-methylformamide and chlorotrimethylsilane with LDA affords synthetically useful yields of the carbamoylsilane. The latter undergoes silyl group exchange at 145°C in the presence of a chlorosilane and CsF.

α-(Dimethylamino)amides from a carbamoylsilane and iminium salts

The reaction of a carbamoylsilane with iminium salts derived from aldehydes lacking α-hydrogens affords the title compounds.

α-Siloxyamides from a carbamoylsilane and carbonyl compounds

Abstract The reaction of a carbamoylsilane with aldehydes or ketones affords α-siloxyamides. The addition reaction is catalyzed by fluoride ion (TBAT, 25–50°C), but proceeds in the absence of catalyst at higher temperatures (50–100°C).

Conversion of some alkenyltrimethylsilanes into silyl enol ethers

Abstract The cycloaddition products (5-trimethylsilylisoxazolines) between alkenyltrimethylsilanes and acetonitrile oxide undergo thermolytic rearrangement-cycloreversion to afford silyl enol ethers of retained stereochemistry vs. the starting alkenylsilanes.