Base-Dependent Cascade Synthesis of Novel Pyrano[3,2-c]coumarin Derivatives from Baylis–Hillman Bromide

5-Oxo-2,3,4,5-tetrahydropyrano[3,2-c]chromene-3-carboxylates derived from 4-hydroxycoumarin and Baylis–Hillman bromides are efficiently obtained in excellent yields within a short time. The transformation is depends on a base, which goes through SN2-SN2 nucleophilic substitution and intramolecular Michael addition. The product structures are confirmed by x-ray crystallography, and a tentative mechanism of the cascade process is presented.