Rhodium-Catalyzed Asymmetric 1,4-Addition of Heteroaryl Cyclic Triolborate to α,β-Unsaturated Carbonyl Compounds

Rhodium-catalyzed asymmetric 1,4-additions of electron-deficient heteroaryl groups to alpha,beta-unsaturated carbonyl compounds were established. The reaction resulted in very low yields due to competitive C-B bond cleavage when arylboronic acids. their pinacol esters, or potassium trifluoroborates were used. However, the corresponding lithium heteroaryl(triol)borates afforded 1,4-adducts With high enantioselectivities up to 97% in the presence of a rhodium(I) catalyst chelated with a chiral BINAP or BIPAM ligand.