Catalytic asymmetric conjugate allylation of coumarins.

A catalytic asymmetric conjugate allylation was successfully developed to synthesize potential pharmacologically active 4-allyl-2-oxochroman skeletons. A dual activation strategy was employed by using N,N′-dioxide-Yb(OTf)3 to activate coumarins and using (CuOTf)2•C7H8 to activate tetraallyltin via transmetalation, respectively. Good yields and enantioselectivities were obtained under mild conditions.