De Novo Synthesis of Tricyclic 5,5-Benzannulated Spiroketals

Rearrangement-Driven Molecular Diversity: Synthesis of Functionalized Pyrones, Orthoesters, and Xanthones from Spiroketals

The reaction of tricyclic 5,5-benzannulated spiroketals with trifluoroacetic acid (TFA) and AlCl₃ furnished benzopyranobenzopyrans, benzofuro-orthoesters, and benzofuroxanthones. Whereas the reaction of tricyclic 5,5-benzannulated spiroketals with TFA produced the pyrones, the reaction with AlCl₃ furnished densely functionalized orthoesters and xanthones. The formation of these products was rationalized by fascinating mechanistic pathways involving semipinacol/α-ketol molecular rearrangements.

Copper-catalyzed synthesis of 1-(2-benzofuryl)-N-heteroarenes from o-hydroxy-gem-(dibromovinyl)benzenes and N-heteroarenes

An efficient method for the synthesis of 1-(2-benzofuryl)-N-heteroarenes is developed from o-hydroxy-gem-(dibromovinyl)benzenes and N-heteroarenes under copper-catalyzed tandem reaction conditions. This methodology displayed a broad substrate scope and high yields in the preparation of a variety of 1-(2-benzofuryl)-N-heteroarenes. Further, 1-(2-benzofuryl)-N-heteroarenes were also applied in the synthesis of polycyclic benzofuro-indolo-pyridine scaffolds under palladium-catalyzed dehydrogenative coupling conditions. Overall, the present tandem approach is general, synthetically advantageous and avoids air-sensitive reagents.

Copper-catalyzed domino synthesis of ynamines

The hitherto unexplored N-alkynylation of electron-withdrawing or protecting group free N-heteroarenes such as indole, carbazole and pyrrole was developed using gem-dibromoalkenes to synthesize ynamines under ligand-free copper-catalyzed domino conditions. The development methodology of ynamines was also applied in the synthesis of enynamines, multi-coupled bis-ynamines, tris-ynamines, and the natural product peyonine, demonstrating its broad synthetic scope and applications.