SYNTHESIS OF BETA,GAMMA-UNSATURATED KETONES THROUGH LIGAND-PROMOTED HYDROIMINOACYLATION OF DIENES BY RH

Chlorobis(isoprene)rhodium(I) (3), prepared by olefin-exchange reaction of chlorobis(cyclooctene)rhodium dimer (2) with isoprene, reacted with benzaldimine 4 to give iminoacylrhodium(III) eta3-1,2-dimethylallyl complex 6. Ligand-promoted reductive elimination of 6 by pyridine and P(OMe)3 produced beta,gamma-unsaturated ketimine 8, which was readily hydrolyzed to give beta,gamma-unsaturated ketone 9. Other methyl branched dienes such as 2,3-dimethylbutadiene, 3-methyl-1,3-pentadiene, 2-methyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3-methyl-1,4-pentadiene and 2-methyl-1,4-pentadiene, were applied the synthesis of beta,gamma-unsaturated ketones. In case of 2,4-dimethyl-1,3-pentadiene, only gamma,delta-unsaturated ketone 25, 1,2-addition product, was obtained, maybe due to the mono-olefin coordination.