Catalytic asymmetric synthesis of diphenylbutazone analogues

The asymmetric Michael addition of diphenylbutazone and its analogues to α,β-unsaturated 2-acyl imidazoles has been developed with a chiral-at-metal Rh(III) complex as a catalyst. The corresponding adducts were obtained in good yields (89–98%) with excellent enantioselectivities (up to >99%). The reaction can be conducted on a gram-scale with a low catalyst loading (0.04 mol%) without impacting its efficiency. Moreover, the adducts can be converted into other useful synthetic building blocks.