Synthesis of Chromeno[3,4-c]pyridines by Rhodium(III)-Catalyzed annulation of coumarinyl ketoxime esters and alkynes

An efficient, scalable synthetic method of chromeno[3,4-c]pyridine scaffolds through redox-neutral [4 + 2] annulation between coumarinyl ketoxime esters and internal alkynes has been developed using the rhodium(III) catalytic system. The present transformation proceeds under mild conditions, features good functional group compatibility and obivates the use of external oxidants. Ready access to pyridine derivatives bearing three carbon substituents is exemplified.