82. Enantioselective reduction of electrophilic C=C bonds with sodium tetrahydroborate and 'semicorrin' cobalt catalysts

Article abstract of DOI:10.1002/hlca.19960790404

'Semicorrin' cobalt complexes, prepared in situ from cobalt(II) chloride and the corresponding ligands, are efficient catalysts for the enantioselective reduction of electrophilic C=C bonds with NaBH₄. The best selectivities (> 90% ee) are achieved with α,β-unsaturated carboxamides and carboxylates. Analogous α,β-unsaturated nitriles, sulfones, and phosphonates afford enantiomenc excesses of 50-70%. Interestingly, in the reduction of α,β-unsaturated sulfones, the highest enantioselectivities were obtained with unsymmetrical 'semicorrins', whereas in all other cases C₂-symmetric 'semicorrins' proved to be superior.