Reactions ofgem-Dibromo Compounds with Trialkylmagnesate Reagents to Yield Alkylated Organomagnesium Compounds
摘要:
The reaction of gem-dibromocyclopropanes 5 with nBu(3)MgLi affords butylated cyclopropylmagnesium species that can be trapped with various electrophiles. The reaction of dibromomethylsilanes 12 requires the addition of a catalytic amount of CuCN.2LiCl for smooth migration of the alkyl groups. The resultant alpha-silylpentylmagnesium compounds 16 react with electrophiles, such as acyl chlorides or alpha.beta-unsaturated ketones to afford alpha- or gamma-silyl ketones, respectively. Treatment of dibromodisilylmethanes with Me3MgLi yields 1-bromo-1,1-disilylethanes 25 that can be converted into 1,1-disilylethenes 29 by dehydrobromination.
Heterosubstituted cyclopropanation of alkenes with organochromium reagents derived from heterosubstituted dihalomethanes, CrCl2, and tetraalkylethylenediamine
stereoselectively fromterminal alkenes by treatment with a reagent derivedfrom iodoform, chromium(II) chloride, and TEEDA (N,N,N′,N′-tetraethylethylenediamine) in THF. Similarly, cyclopropylsilanes and cyclopropylboronic esters are obtained by using R3SiCHI2, and a combination of Cl2CHB(OR)2 and LiI instead of iodoform, respectively. The heterocyclopropanation occurs selectively at terminaldoublebonds, and
Preparation of Cyclopropylsilanes from Terminal Alkenes with Organochromium Reagents
作者:Kazuhiko Takai、Masato Hirano、Shota Toshikawa
DOI:10.1055/s-2004-825612
日期:——
Treatment of terminal alkenes with Me3SiCHI2, CrCl2, and TMEDA in THF at 25 °C gives cyclopropylsilanes in good to excellent yields. The trans:cis ratios of the cyclopropylsilanes are improved by replacing Me3SiCHI2 with i-Pr3SiCHBr2 and LiI.
Silyl-substituted bis(bromozincio)methanes (RMe2SiCH(ZnBr)2; R = Me, Ph, and p-MeO-C6H4), prepared from the corresponding dibromides by Pb catalyzed reaction with zinc, reacted stepwise with two different electrophiles, R1X and E+, yielding R1-CH(SiMe2R)-E.
Magnesium-bromine exchange to provide the 1-bromo-1-silylmethylmagnesium species is mediated by treatment of dibromomethylsilane with an trialkylmagnesate reagent. The addition of a copper catalyst induces facile migration of an alkyl group to afford an α-silylalkylmagnesium compound, which furnishes α-silyl ketones in good yield upon treatment with acyl chloride.
L. , LARSON G.; TORRES E.; MORALES C. B.; MCGARVEY G. J., ORGANOMETALLICS, 5,(1986) N 11, 2274-2283
作者:L. , LARSON G.、 TORRES E.、 MORALES C. B.、 MCGARVEY G. J.