Copper(II)-Catalyzed (3+2) Cycloaddition of 2<i>H</i>-Azirines to Six-Membered Cyclic Enols as a Route to Pyrrolo[3,2-<i>c</i>]quinolone, Chromeno[3,4-<i>b</i>]pyrrole, and Naphtho[1,8-<i>ef</i>]indole Scaffolds

Abstract

A method for the [2+3] pyrroline annulation to the six-membered non-aromatic enols using 3-aryl-2H-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-c]quinoline, chromeno[3,4-b]pyrrole, and naphtho[1,8-ef]indole derivatives in good to excellent yields from enols of the quinolin-2-one, 2H-chromen-2-one, and 1H-phenalen-1-one series.

Keywords

• azirines
• pyrrolines
• cycloaddition
• annulation
• copper catalysis