Convenient Synthesis of 2, 3, 9, 10-Tetraoxygenated Protoberberine Alkaloids and Their 13-Methyl Alkaloids

Abstract

New and convenient synthesis of 2, 3, 9, 10-tetraoxygenated protoberberine alkaloids and their 13-methyl alkaloids through the same intermediates was developed. Acylation of the brominated benzylphenethylamine (13) with α-chloro-α-(methylthio)acetyl chloride, followed by cyclization with stannic chloride, furnished tha key intermediates 4-methylthio-3-phenethylisoquinolin-3-ones (14), which were methylated to provide their methyl derivatives (17). Both isoquinolin-3-ones (14, 17) were easily transformed into protoberberine alkaloids (16) and their 13-methyl alkaloids (21) in good yield.