Me-BIPAM for the Synthesis of Optically Active 3-Aryl-3-hydroxy-2-oxindoles by Ruthenium-catalyzed Addition of Arylboronic Acids to Isatins

A chiral O-linked C2-symmetric bidentate phosphoramidite (Me-BIPAM) was found to be efficient for the ruthenium-catalyzed addition of arylboronic acids to isatins. Asymmetric synthesis of 3-aryl-3-hydroxy-2-oxindoles by 1,2-addition of arylboronic acids to isatins was carried out in the presence of [RuCl2(PPh3)3]/(R,R)-Me-BIPAM and KF, resulting in an enantioselectivity as high as 90?% ee. It was found that the reaction with N-protected isatins proceeds with high yields and good enantioselectivities. The best protective groups on the nitrogen atom were different depending on the substituents on the aromatic ring. The use of a N-benzyl group resulted in excellent enantioselectivities in many substrates compared with other groups.