Although the reaction of heterosubstitutedallyliccarbanions (2) with aldehydes generally produces a mixture of the γ- and α-adducts (4 and 3), syn-3 and anti-3 can be prepared either exclusively or predominantly by the proper choice of the organometallic compound added.
Gallium-mediated highly regioselective reactions of trimethylsilylpropargyl bromide and trimethylsilylallyl bromide with carbonyl compounds
作者:Ying Han、Yao-Zeng Huang
DOI:10.1016/s0040-4039(00)78562-5
日期:1994.12
One-pot reactions of gallium powder, trimethylsilylpropargyl bromide, aldehydes or ketones in the presence of KI and LiCl show very high acetylenic selectivity and under the same conditions, trimethylsilylallyl bromide also exhibits very high selectivity favoring α-adducts.
Regio- and stereo-selective coupling between trimethylsilyl allyl carbanions and aldehydes is achieved in the presence of an additive, ‘M’; use of R2BCl or EtAlCl2 as the additive gives the threo isomer (3) predominantly, while use of Bu3SnCl–BF3 affords the erythro isomer exclusively.
Various gamma-heteroatom-substituted allylindium reagents were prepared, and their reactions with carbonyl compounds were examined. The reaction of 1,3-dibromopropene with metallic indium gave two types of organoindium species, gamma-bromoallylindium and allylic diindium reagents. While the former gave 2-phenyl-3-vinyloxirane upon the coupling with benzaldehyde, the latter gave 1-phenylbut-3-en-1-o1. 1-Iodo-3-bromopropene gave the homoallylic alcohol exclusively. gamma-Alkoxyallylindium reagents were prepared by treating the corresponding gamma-alkoxyallyllithium with indium trichloride and reacted with benzaldehyde to give vic-diol mono ethers in high yields with good syn selectivity. gamma-(Trimethylsilyl)allylindium and alpha,gamma-disubstituted allylindium reagents were also prepared via transmetalation with the corresponding allyllithium.