Synthesis of 6-Oxaellipticine, 5,11-Dimethylbenzofuro[2,3-g]isoquinoline, and related heterocycles

Abstract

6-Oxaellipticine, 5,11-dimethylbenzofuro[2,3-g]isoquinoline, has been synthesized by a three-step procedure from 1,4-dimethyldibenzofuran utilizing a Pomeranz-Fritsch cyclization. The structures of the intermediate 2-formyl-1,4-dimethyldibenzofuran and of 6-oxaellipticine were confirmed by application of the nuclear Overhauser effect. The parent heterocycle, benzofuro[2,3-g]isoquinoline, has been prepared similarly from dibenzofuran, and this product converted successively into 2-methylbenzofuro[2,3-g]isoquinolinium iodide, 2-methyl-1,2,3,4- tetra-hydrobenzofuro[2,3-g]isoquinoline, and 2-methyl-1-oxo-1,2,3,4- tetrahydrobenzofuro-[2,3-g]isoquinoline.     Benzothieno[3,2-h]isoquinoline has been prepared from 4- formyldibenzo-thiophen formed together with the 2-formyl derivative by reaction of dibenzothiophen with dichloromethyl methyl ether in the presence of stannic chloride.