Transition Metal-Catalyzed Synthesis of 3-Coumaranone-Containing NH-Aziridines from 2H-Azirines: Nickel(II) versus Gold(I)

A catalytic nucleophilic addition reaction of 3-hydroxybenzofuran-2-carboxylic acid derivatives to 2H-azirines for the high-yield synthesis of NH-aziridines with a 3-coumaranone substituent has been developed. The Ph3PAuNTf2-catalyzed reaction is diastereoselective to give predominantly (RS,SR)-isomer of aziridine in good yield. The Ni(hfacac)(2)-catalyzed reaction affords aziridines in up to 98% yield and low or moderate diastereoselectivity, which in some cases is opposite to that observed for the gold(I)-catalyzed reaction. The Ph3PAuNTf2 works well for sterically hindered azirines as well as benzofurans bearing electron-withdrawing groups, whereas Ni(hfacac)(2) is the catalyst of choice for the preparation of aziridines having diazoacetyl substituent. The latter compounds can serve as substrates for the synthesis of fused aziridines via Buchner ring expansion reaction.