Asymmetric conjugate additions to 1,1′-diactivated cyclic enonesa-comparative study

A study of copper-phosphoramidite-catalysed ZnR2 and AlR3 additions to 1,1'-dicarbonyl-activated cyclic Michael acceptors has revealed high enantioselectivities for AlR3 (R = Me, Et) 1,4-addition to a range of 3-acylcoumarins (85-98% ee, trans:cis similar to 90:10) using commercial OF readily available ligands. Large substituents at the 6-position, and to some extent at the 5-position, of the coumarin are less well tolerated, nor is truncation of the coumarin motif to a comparable 2-acylcyclohexenone (ee values up to 78%). (C) 2009 Elsevier Ltd. All rights reserved.