coupling reaction of aromatic and aliphatic ketones including acyclic aliphatic ketones proceeded smoothly to give the corresponding pinacols in good to high yields below room temperature by the combined use of titanium(II) chloride and zinc in the presence of pivalonitrile. Meso-selective formation of the coupling products was observed in the cases with some acyclic aliphatic ketones.
Mischmetall, an alloy of the light lanthanides, has been used in a variety of organicreactions, either as a coreductant in samarium(II)-mediated reactions (Barbier and Grignard-type reactions, pinacoliccouplingreactions) or as the promoter of Reformatsky-type reactions. It has been also employed as the starting material for easy syntheses of lanthanide trihalides, the reactivity of which has been
Trimethylsilyl chloride-accelerated reduction and pinacol coupling of carbonyl compounds by means of samarium diiodide
作者:Toshio Honda、Miho Katoh
DOI:10.1039/a607774i
日期:——
The combination of samarium diiodide (SmI
2
) and
trimethylsilyl chloride (Me
3
SiCl) in THF–HMPA is found to
accelerate the reduction of sterically hindered and enolisable ketones,
and also to accelerate pinacolisation of the carbonyl compounds depending
on the reaction conditions.
A new convenient preparation of samarium dibromide in THF is reported. Pinacolcoupling reactions using SmBr2 in catalytic amounts together with mischmetall as a coreductant have been performed with a variety of carbonylcompounds.
Cerium metal activated by a trace of iodine reacted smoothly with alkyl, allyl, and aryl iodides to give the corresponding organocerium reagents. The reaction of the organocerium reagents thus prepared in situ with carbonyl compounds gave not only Grignard-type adducts but also reduction and reductive coupling products.