Simultaneous formation of 8H-Isoquino[2,1-b][2,7]naphthyridin-8-ones and 13H-Pyrido[4',3':3,4]pyrrolo[2,1-b][3]benzazepin-13-ones, a novel potential alkaloidal system

Abstract

Condensation of 3,4-dihydro-6,7-dimethoxyisoquinoline (4) with 4-methylnicotinoyl chloride (12) in refluxing pyridine gives 5,6,13,13a-tetrahydro-2,3-dimethoxy-8H-isoquino[2,1-b][2,7] naphthyridin-8-one (11), along with some of its 13,13a-didehydro derivative 7. A similar reaction of 4 with 4-(chloromethyl)nicotinoyl chloride (14) affords, in addition to 7, the isomeric product 10,11-dihydro-7,8-dimethoxy-13H-pyrido[4',3':3,4]pyrrolo[2,1- b][3]benzazepin-13-one (3). Analogous pairs of products are obtained from 3,4-dihydro-6,7-(methylenedioxy)- and 3,4-dihydro-6,7,8-trimethoxy-isoquinolines (15 and 18, resp.). The structure of 3 was established by extensive NMR data and confirmed by single-crystal X-ray studies. Structure 7 has the ring system of the Alangium alkaloids like alangimarinc (1), while the isomeric ring system 3 is predicted to be present in nature on biogenetic reasoning.