Highly enantioselective cyclopropanation of styrenes and diazoacetates catalyzed by 3-oxobutylideneaminatocobalt(II) complexes, Part 1. Designs of cobalt complex catalysts and the effects of donating ligands

Highly enantioselective cyclopropanation of styrene derivatives and diazoac etates was effectively catalyzed by reasonably designed 3-oxobutylideneamin atocobalt(II) complexes, whose ligands were prepared from 1,2-dimesitylethy lenediamine and alkyl 3-oxobutanoates. The steric demand of the diamine uni t of the complexes seriously influenced the enantioselectivity, and the est er groups on their side chains somewhat improved the trans-selectivity. Add ition of a catalytic amount of N-methylimidazole significantly accelerated the reaction and enhanced the enantioselectivity due to its coordination to the center cobalt atom of the complex as an axial ligand. Alcoholic or aqu eous alcoholic solvents were also effective particularly for the cyclopropa nation of 1-substituted 1-phenylethylenes to achieve high enantioselectivit y in aqueous methanol.