Kinetic Resolution of 2H-Azirines by Asymmetric Allylation Reactions

A practical and efficient method for kinetic resolution of azirines has been achieved via asymmetric allylations of racemic 2H-azirines with boron allylation reagents enabled by Bi(OAc)3/chiral phosphoric acid catalysis. A broad range of azirine substrates with electron-withdrawing and electron-donating groups at the two aromatic rings, as well as the different allyl boron reagents, were well tolerated in this methodology, providing high kinetic resolution performance (with an s-factor of up to 127) under very mild reaction conditions with only 2 mol % catalyst loading. In addition, the synthetic utility of the protocol was proved by the scaled-up reaction and transformations of the product. Computational studies suggested that the various weak interactions are essential for enantioselectivity. Moreover, the effect of different metal acetates and counteranions on the reaction outcome was also interpreted by the calculations.