Copper(II)-Catalyzed (3+2) Cycloaddition of 2-Azirines to Six-Membered Cyclic Enols as a Route to Pyrrolo[3,2-]quinolone, Chromeno[3,4-]pyrrole, and Naphtho[1,8-]indole Scaffolds.

A method for the [2+3] pyrroline annulation to the six-membered non-aromatic enols using 3-aryl-2-azirines as annulation agents is developed in the current study. The reaction proceeds as a formal (3+2) cycloaddition via the N1-C2 azirine bond cleavage and is catalyzed by both Cu(II) and Cu(I) compounds. The new annulation method can be applied to prepare pyrrolo[3,2-]quinoline, chromeno[3,4-]pyrrole, and naphtho[1,8-]indole derivatives in good to excellent yields from enols of the quinolin-2-one, 2-chromen-2-one, and 1-phenalen-1-one series.