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

Abstract

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.

Keywords:

• Baylis–Hillman bromides
• intramolecular Michael addition
• nucleophilic substitution
• pyrano[3,2-c]coumarin
• X-ray crystallography

ACKNOWLEDGMENT

We are grateful for the financial support from the Science and Technology Project of Zhejiang Province (No. 2008C21033).

Notes

^a The reaction was carried out in refluxing acetone with 1.2 eq base.

^b Refers to the isolated mixture of 3a/4a.

^c Determined by ¹H NMR.

^d The reaction was executed at room temperature.

^e No desired product but side product was isolated.

^f No reaction and bromide was quantitatively recycled.

^g No desired product but bromide was completely consumed.

^a Isolated overall yield of the mixture of 3 and 4.

^b Determined by ¹H NMR.