Atom-controlled divergent synthesis of spiro and fused rings via base-catalyzed chemoselective annulation

Abstract

Annulation reactions are recognized for their efficiency in constructing complex cyclic compounds with multiple substitutions, aligning well with green chemistry principles. Herein, we report a transition-metal-free, chemodiverse cycloaddition reaction employing allylamines as [C,N] synthons that react with azadienes in an environmentally benign manner. The protocol has been applied to benzofuran- and indanone-derived azadienes via [3 + 2] cycloadditions, and to benzothiophene-derived azadienes via [3 + 4] cycloadditions, yielding a series of spirobenzofurans, spirotetrandrines, and benzothiophene-diazepines with high diastereoselectivity. In addition to avoiding the use of toxic transition metals, the process demonstrates the potential for further functional group transformations of the cycloaddition products, paving the way for the sustainable generation of valuable intermediates.