Organometallic reaction in ionic liquids: Alkylation of carbonyl compounds with organozinc and organoaluminium reagents

Alkylation of carbonyl compounds with diorganozinc, organozinc halides and organoaluminium reagents has been conducted in ionic liquids. Systems studied included solvents such as N-butylpyridinium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate. Interestingly, reactivities of organometallics towards ionic liquids were revealed, yielding the imidazolylidene zinc complex formation in the case of alkylation with diethylzinc. Thus, different ways of ionic liquid preparations and purification methods were studied. The reaction between diethylzinc and aldehyde proceeded cleanly with high yield. This is in contrast to the reaction in aqueous media where diethylzinc is hydrolyzed readily, or in conventional volatile organic solvents where the addition of diethylzinc to aldehyde is generally sluggish and gives a low yield.;Besides, we have demonstrated that the trialkylaluminium reagents could be used to alkylate carbonyl compounds giving dimethylaluminium alkoxides as the major reaction products. And it is believed that triorganoaluminium reagents react with carbonyl compounds in both solventless and ionic liquid conditions involving the first order four-center transition state.;Generation of organozinc reagents in situ in carrying out other zinc mediated alkylation reactions has also been attempted. Preliminary success of the in situ preparation of ethylzinc and isopropylzinc halide has been achieved in ionic liquid.