Synthesis of Isoprenyl Chalcone “Sophoradin” through Claisen Rearrangement

Abstract

Sophoradin (I) [2', 4, 4'-trihydroxy-3, 3', 5-tris (3-methyl-2-butenyl) chalcone] which had been isolated from “Guang-Dou-Gen” (the root of Sophora subprostrata CHUN et T. CHEN) was synthesized through Claisen rearrangement. The reaction of p-hydroxybenzaldehyde and 3-chloro-3-methyl-1-butyne (III) gave 4- (1, 1-dimethylpropargyloxy) benzaldehyde (VIII), which was catalytically hydrogenated over Lindlar catalyst to afford 4- (1, 1-dimethylallyloxy) benzaldehyde (IX). IX was converted to 4-hydroxy-3-(3-methyl-2-butenyl) benzaldehyde (X) by Claisen rearrangement. The reaction of X and III gave 3-(3-methyl-2-butenyl)-4-(1, 1-dimethylpropargyloxy) benzaldehyde (XI). Condensation of 2-hydroxy-4- (1, 1-dimethylpropargyloxy) acetophenone (IV) and XI in alkaline solution gave a chalcone (XIII), which was catalytically hydrogenated over Lindlar catalyst to give 2'-hydroxy-4, 4'-bis (1, 1-dimethylallyloxy)-3-(3-methyl-2-butenyl) chalcone (XIV). XIV was converted to I by Claisen rearrangement.