Highly enantioselective cyclopropanation of styrenes and diazoacetates catalyzed by 3-oxobutylideneaminatocobalt(II) complexes, Part 2. Semiempiricalanalysis of diastereo and enantioselectivities

A semiempirical analysis using the PM3(tm) method was performed on the 3-ox obutylideneaminatocobalt(II) complexes-catalyzed cyclopropanation. Although the energy diagram calculated by the PM3(tm) method had a contradiction, w here the product was less stable than the reactant, the structures and the energies of the reactant and the transition state obtained by the PM3(tm) m ethod could be relatively reliable by comparing with the results based on t he density functional theory. Analysis of the transition states by the PM3( tm) method indicated that the olefin approached parallel to the cobalt-carb ene bond with bisecting an O-1-CO-O-2 angle. It was revealed that the trans ition state affording the (1S,2S)-arylcyclopropanecarboxylic acid ester cor responding to the (1S,2S)-cobalt complex was the most stable, because of th e lowest steric repulsion among the aryl group of the diamine unit, the est er moiety, and the approaching olefin. It was clarified that the enantiosel ectivity occurred due to the repulsion between the aryl group of the diamin e unit and the ester moiety and that the diastereoselectivity was controlle d by the repulsion between the ester moiety and the approaching olefin.