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.
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.