2 H-Azirines as C-C Annulation Reagents in Cu-Catalyzed Synthesis of Furo[3,2- c]quinolone Derivatives.

A method of furo-annulation of 4-hydroxy-2-oxoquinoline-3-carboxylates with 3-arylazirines under Cu(II) catalysis was developed to synthesize a variety of 2,3-dihydrofuro[3,2- c]quinolones bearing a carbamate group at the C2 position. The reaction involves an azirine ring opening across the N-C2 bond and formation of a dihydrofuran ring with the inclusion of two azirine carbon atoms, accompanied by a shift of the ester group to the nitrogen. The discovered reaction is the first example of the use of 2 H-azirines for furo-annulation.