A Ring Destruction Approach to Some Benzo-Fused Medium-Sized Heterocycles by Means of Cyanogen Bromide under Solvolytic Conditions - X-Ray Structure of a 1 H-2, 6-Benzoxazecine-6-carbonitrile and a 2 H-3, 6-Benzoxazecine-6-carbonitrile Derivative

Reaction of the reduced pyrrolo[2, 1-a]isoquinoline amine (1a) with cyanogen bromide in the presence of methanol gave the medium-ring cyanamide derivative 7, 9, 10-trimethoxy-2, 3, 4, 5, 6, 7-hexahydro-1 H-3-benzazonine-3-carbonitrile (2a). Analogous products were also obtained from reaction of the reduced 5 H-oxazolo[2, 3-a]isoquinoline, 27 H-benzo[a]quinolizine, 2 H, 6 H-[1, 3]oxazino[2, 3-a]isoquinoline and [1, 4]oxazino[3, 4-a]isoquinoline derivatives (1b-e), whereas the reduced 3 H-oxazolo[4, 3-a]isoquinoline and 5 H-oxazolo[2, 3-a]isoquinoline derivatives (1f) and (8) gave 1-(2, 4-dioxapentyl)-6, 7-dimethoxy-1, 2, 3, 4-tetrahydroisoquinoline-2-carbonitrile (5a) and N-[2-(2-benzoyl-4, 5-dimethoxyphenyl)ethyl]-N-methylcyanamide (9) respectively, the latter in low yield. The medium-sized heterocyclic derivatives (2f-h) were also obtained from cyanogen-bromide-mediated water solvolysis reactions of (1a), (1c) and (1e). The cyanamides (2a-h), (5a) and (9) have been converted into the respective tertiary amine derivatives (3a-h), (5c) and (11), with concomitant reduction of the carbonyl group in the last case. The crystal and molecular structure of 1, 10, 11-trimethoxy-3, 4, 5, 6, 7, 8-hexahydro-1 H-2, 6-benzoxazecine-6-carbonitrile (2d) and 1-hydroxy-10, 11-dimethoxy-1, 4, 5, 6, 7, 8-hexahydro-2 H-3, 6-benzoxazecine-6-carbonitrile (2h) have been determined by single-crystal X-ray methods.