Synthesis of dl-4-Hydroxycrebanine

Abstract

4-Hydroxycrebanine (2), a natural product from Stephania sasakii HAYATA, was synthesized via 1-(6'-bromo-2', 3'-dimethoxybenzyl)-4-hydroxy-2-methyl-6, 7-methylenedioxy-1, 2, 3, 4-tetrahydroisoquinoline (17), which was obtained by Bobbitt's modification of the Pomeranz-Fritsch cyclization of N-[2-(6'-bromo-2', 3'-dimethoxyphenyl)-1-(3, 4-methylenedioxy phenyl) ethyl] aminoacetaldehyde diethyl acetal (12). Irradiation of the compound (17) with the cis relationship of C₁-H and C₄-H gave dl-4-hydroxycrebanine (2) and its isomer (2a). The stereostructures of the two isomers were established firmly by direct comparison of the proton nuclear magnetic resonance spectra.