Tandem Copper-Catalyzed Regioselective <i>N</i>-Arylation–Aza-Michael Addition: Synthesis of Tetracyclic 5<i>H</i>-Benzothiazolo[3,2-<i>a</i>]quinazoline Derivatives
Jyoti M. Honnanayakanavar, Battu Harish, Jagadeesh Babu Nanubolu, Surisetti Suresh
Abstract
A copper-catalyzed tandem process integrating regioselective N-arylation, followed by aza-Michael addition, is disclosed using 2-aminobenzothiazoles and ortho-halo cinnamic acid congeners. This process generated diverse tetracyclic 5H-benzothiazolo[3,2-a]quinazoline derivatives in moderate to good yields. The present tandem reaction appears to proceed through concomitant ring opening of 2-aminobenzothiazole and S-arylation to give the ortho-cyanamide-substituted diaryl thioether intermediate. The thus generated intermediate likely undergoes an unprecedented Truce–Smiles-type rearrangement involving S- to N-aryl migration, followed by reformation of the thiazole ring and intramolecular aza-Michael addition to furnish the title products.