Origin of Regio and Stereoselectivity in Conjugate Addition Reactions

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We have reported the successful chiral ligand-mediated asymmetric 1,2- and 1,4-addition reactions of organolithiums to various imines of aryl and alpha, beta-unsaturated aldehydes Thus, organo-lithiums add to the cyclohexylimines 1,2 (R=c-C6Hll) in 1,4-fashion to give, after hydrolysis, the corresponding aldehydes in up to 99% ee and in high to good yields. On the other hand, the reactions with arylimines exclusively afford 1,2-adducts in up to 90% ee and in nearly quantitative yields, giving us a good method for the preparation of chiral amines. It is also interesting in that the reactions with both cyclohexyl- and arylimines of 1-fluoronaphthalene-2-carbaldehyde exclusively proceed in 1,4-fashion to provide nucleophilic aromatic substitution products in high yields. Since deep understanding of the factors governing regioselectivity is a long-standing problem and essential for further development of the much more effective catalytic asymmetric reactions of the ene-imines. we carried out molecular orbital calculations and revealed that the experimentally observed regioselectivity is rationalized by the relative magnitude of the LUMO coefficients.