Base-Promoted Cascade Reactions of 3-(1-Alkynyl)chromones with Pyridinium Ylides to Chromeno[2,3-d]azepine Derivatives

A base-promoted cascade reaction of 3-(1-alkynyl)chromones with pyridinium ylides has been developed to afford a novel chromeno[2,3-d]azepine scaffold in an efficient and economic manner. This tandem process involves multiple reactions including a Michael addition/deprotonation/alkyne–allene isomerization/cyclization and the subsequent 1,2-addition under mild conditions without a transition metal catalyst.