155 16. 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-l3-ones,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-8~-isoquino[2,l-b][2,7]naphthyridin-8-one (Il), 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,l l-dihydro-7,8-dimethoxy-13H-pyrido[4',3':3,4]pyrrolo[2,lb][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 alangimarine (l), while the isomeric ring system 3 is predicted to be present in nature on biogenetic reasoning. Introduction. -The alkaloids of Alangium lumarckji THW. represented by alangimarine (1) [ 11 have the interesting 8H-isoquino[2,1-b][2,7]naphthyridin-8-one ring system isosteric with 8-oxoprotoberberines [2]. Alkaloids of the latter group like prechilenine, in the correct oxidation state, were found to rearrange in nature to the isomeric isoindolobenzazepines, e.g. chilenine [3]. Aporhoedane (2) having this ring system was known earlier [4] and was synthesized [5]. Similar biogenetic transformations of Alangium alkaloids can give rise to natural products with the pyrido-[4',3':3,4]pyrrolo[2,l-b][3]benzazepine ring system, typified by 3 which are hitherto unkown in nature or by synthesis.The first approach to the synthesis of isoquinonaphthyridines of type 1 predated the isolation of the alkaloids and involved the irradiation of the enamide of 3,4-dihydro-1methylisoquinoline with nicotinoyl chloride [6]. Subsequently, this reaction was shown to occur also thermally but found to suffer from nonregiospecificity [7]. Notwithstanding this handicap, the thermal cyclization approach was successfully applied to the synthesis of alamarine, isoalamarine, and alamaridine [8]. Alternative approaches which do not suffer from the problem of nonregiospecificity start from the 3,4-dihydro-6,7-dimethoxy-') Present address:
