Cascade Construction of Cinnoline and Furanone Skeletons from Phenylhydrazine and Maleimide Featuring a Formal Oxygen Swap.

Both cinnoline and furanone are the pivotal skeletons of numerous natural products and pharmaceuticals. While a number of reliable methods for the respective synthesis of cinnoline or furanone derivatives are currently available, concurrent construction of these two privileged scaffolds in one pot has not been disclosed. We report herein a concise and convenient synthesis of cinnoline fused furanone from the easily obtainable and economically sustainable phenylhydrazine and maleimide. Mechanistically, the formation of product involves C-H bond activation-initiated cinnoline ring forming along with the maleimide ring opening, followed by an intramolecular O-nucleophilic addition to form the furanone skeleton. Notably, this tandem annulation process is realized via C-H/C-N/C-N bond activation and C-C/C-N/C-O bond formation featuring an interesting formal oxygen swap. This novel reaction not only enriches the chemical space of phenylhydrazine and maleimide as versatile synthetic building blocks, but also provides a reliable approach toward the biologically promising fused N/O heterocycles with advantages such as simple substrates, good efficiency, free of external oxidant, high atom-economy and ready scalability.