Photosolvolysis of bridgehead quaternary ammonium salts. II. Synthesis of some 2,5-Benzoxazonine derivatives and attempted synthesis of the 1,2,4,5,6,7-Hexahydro-3,5-benzoxazonine system

Abstract

The medium-ring heterocyclic derivative 1,9,10-trimethoxy-5-methyl-1,3,4,5,6,7-hexahydro-2,5- benzoxazonine (6a) was obtained in fair yield from photosolvolysis of 8,9-dimethoxy-4-methyl- 2,3,6,10b-tetrahydro-5H-oxazolo[2,3-a]isoquinolinium iodide (5a) in methanol, together with minor amounts of 3,9,10-trimethoxy-5-methy1-1,3,4,5,6,7-hexahydro-2,5-benzoxazonine (8) and 2-[N-2- {2-(dimethoxymethyl)-4,5-dimethoxyphenyl}ethyl-N-methylamino]ethanol (7). Photosolvolysis products analogous to (6a) were obtained from other related lob-substituted oxazolo[2,3-aliso-quinolinium iodides in high to low yields depending upon the nature of the angular substituent and the presence or absence of substituents in the fused aromatic ring. No methanolysis of the methiodide salts (5a-f) was observed in the absence of ultraviolet irradiation, whereas 1-(2-ethenyl- 4,s-dimethoxypheny1)ethanone (14) was formed on heating (5b) with methanolic potassium hydroxide. Attempted synthesis of 1,2,4,5,6,7-hexahydro-3,5-benzoxazonine derivatives by photosolvolysis of 8,9-dimethoxy-4-methyl-1,5,6,10b-tetrahydro-3H-oxazolo[4,3-a]isoquinolinium iodide (17) in methanol or water was unsuccessful, ring-opened products being obtained in low yield instead.