A high yield synthesis of N-formyl-1-methylnordihydrothebainone

Abstract

Acid-catalysed cyclisation of 2-formyl-1,2,3,4,5,8-hexahydro-1-(5-hydroxy-4-methoxy-2-methylbenzyl)-6-methoxyisoquinoline (Ia) gave N-formyl-1-methyl-nordihydrothebainone (IIa); the 2-methyl substituent in the benzyl radical prevents the formation of the undesirable isomer (IIIa) and gives a much higher yield than analogous cyclisations.