Palladium-Catalyzed Tandem Carbene Migratory Insertion and Intramolecular Cyclization: Synthesis of Chromeno[4,3‑<i>b</i>]chromene Compounds

Chromeno­[4,3-b]­chromene is a ubiquitous structural motif found in various pharmaceuticals and biologically active compounds. A concise palladium-catalyzed reaction of vinyl iodides and salicyl N-tosylhydrazones has been achieved to afford a series of compounds containing the chromeno­[4,3-b]­chromene scaffold in moderate to high yield. This tandem reaction involves palladium­(II) carbene migratory insertion and intramolecular cyclization assisted by an O nucleophile and tolerates various functional groups.