Photosolvolysis of Bridgehead Quaternary Ammonium Salts. III. Synthesis of Some 3-Benzazecine, 1H-2,6-Benzoxazecine and 2H-3,6-Benzoxazecine Derivatives and a 2H-1,4-Oxazocine Derivative

Abstract

Photosolvolysis of a mixture of cis - and trans-9,10-dimethoxy-5-methyl- 1,3,4,6,7,11b-hexahydro-2H-benzo[a] quinolizinium iodide (2) in methanol gave, after workup, a very low yield of 8,10,11-trimethoxy-3-methyl- 1,2,3,4,5,6,7,8-octahydro-3-benzazecine (3a). Similarly 1,10,11 trimethoxy-6-methyl-3,4,5,6,7,8-hexahydro-1H-2,6-benzoxazecine (8a) and 1,10,11-trimethoxy-6-methyl-1,4,5,6,7,8-hexahydro-2H-3,6-benzoxazecine (16a) were obtained in fair and low yields respectively from the N- methyl tetrahydro-2H,6H-[1,3] oxazino [2,3-a] isoquinolinium (7a) and hexahydro [1,4] oxazino [3,4-a] isoquinolinium (15) iodide precursors; a 1- methyl derivative (8b) of (8a) was also prepared. The ring-opened products 3-[N-2-{(4,5-dimethoxy-2-dimethoxymethyl)-phenyl}ethyl-N-methyl]aminopropan-1-ol (9a) and 3-[N-2-{(4,5-dimethoxy-2-1′,1′- dimethoxyethyl )-phenyl}ethyl-N-methyl]aminopropan-1-ol (9b) were also obtained from the [1,3] oxazino [2,3-a]- isoquinolinium salt derivatives. Photolysis of (2) and 9,10-dimethoxy-5-methyl-1,3,4,6,7,11b-hexa-hydro[1,4] oxazino [3,4-a] isoquinolinium iodide (15) in acidified aqueous solution afforded, after workup, the benzazecin-8-ol (3b) and hexahydro-2H-3,6-benzoxazecin-1-ol (16b) products respectively, but again in very low yield. Some mechanistic rationalizations of these results are given.Photosolvolysis of 7a-(3,4-dimethoxy)phenyl-4-methyl-2,3,5,6,7,7a- hexahydropyrrolo [2,1-b] oxa-zolium iodide (22) in methanol afforded a high yield of 8-methoxy-4-methyl-8-(3,4-dimethoxy)-phenyl-3,4,5,6,7,8- hexahydro-2H-1,4-oxazocine (24) in a new ring-destruction approach to this ring system. From 13C n.m.r . data, the twist-boat-chair conformation was tentatively assigned to (24) in (D)chloroform solution.