Total Synthesis of Daphneticin, a Coumarinolignoid

Abstract

Daphnetin (3) was transformed with excess benzyl chloride into 7, 8-dibenzyloxycoumarin (4), which on treatment with trifluoroacetic acid in benzene or aluminum chloride in benzene gave 8-benzyloxy-7-hydroxycoumarin (5) in good yield. Condensation of 5 and ethyl 2-bromo-3-(4-acetoxy-3, 5-dimethoxyphenyl)-3-oxopropionate (9), prepared from ethyl benzylsyringoylacetate (7) in two steps, in the presence of sodium hydride afforded 10 in good yield, and the condensation product (10) was then reduced with lithium borohydride to yield a mixture of the diols (11a, b). Treatment of the diols with 36% hydrochloric acid in acetic acid provided daphneticin (1) in 68% yield.