Activation of iodosobenzene by catalytic tetrabutylammonium iodide and its application in the oxidation of some isoquinoline alkaloids

Oxidation of N-methyltetrahydroisoquinolines with iodosylbenzene in the presence of a catalytic amount of tetrabutylammonium iodide in various solvents afforded N-methyl-2H-3,4-dihydroisoquinol-1-ones in almost quantitative yields. The application of this finding to the oxidation of other isoquinolines, including tetrahydroisoquinolines, lycorine diacetate, and benzyltetrahydroisoquinolines, also afforded the corresponding lactams in good yields, however, accompanied by a few minor byproducts. Under similar conditions, tetrahydroberberine gave a rearranged compound, berberal, as the major product, accompanied by 8-oxoberberine and berberine.