Synthesis of Functionalized Chromene and Chroman Derivatives via Cesium Carbonate Promoted Formal [4 + 2] Annulation of 2′-Hydroxychalcones with Allenoates

A new strategy has been established for the synthesis of functionalized chromene and chroman derivatives via a Cs ₂ CO ₃ -catalyzed domino addition of 2′-hydroxychalcone derivatives with allenoates, which can serve as a general avenue for the construction of multireplaced chromene derivatives. Chemoselectivity of this synthesis was found to depend on substituents on substrates. Good to excellent yields were achieved under simple and mild conditions at room temperature.