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

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 allylamine 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 cycloaddition products, paving the way the sustainable generation of valuable intermediates.