Enone structure as a probe to Lewis acid carbonyl binding in copper-catalysed asymmetric conjugate addition

Systematic changes in the substitution pattern of linear enones ((RCOCH)-C-1=CHR2) helps identify the reactive conformation (s-trans versus s-cis) of the enone in copper-catalysed asymmetric 1,4-ZnEt2 addition. Pointers to the binding mode of the Lewis Acid (syn or anti to the 'ene' function) are also gathered. Enantioselectivities of up to 79% have been realised in these reactions. (C) 2000 Elsevier Science Ltd. All rights reserved.