Convenient synthesis of 2,3,9,10-tetraoxygenated protoberberine alkaloids and their 13-methyl alkaloids

New and convenient synthesis of 2,3,9,10-tetraoxygenated protoberberine alk aloids and their 13-methyl alkaloids through the same intermediates was dev eloped. Acylation of the brominated benzylphenethylamine (13) with alpha-ch loro-alpha-(methylthio)acetyl chloride, followed by cyclization with stanni c chloride, furnished the key intermediates 4-methylthio-3-phenethylisoquin olin-3-ones (14), which were methylated to provide their methyl derivatives (17). Both isoquinolin-3-ones (14, 17) were easily transformed into protob erberine alkaloids (16) and their 13-methyl alkaloids (21) in good yield.