Benzomorphan related compounds. XIII. Syntheses of 2,6‐methanopyrrolo[1,2‐d] [1,4]diazocines

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Abstract
Two alternative syntheses of 2,6‐methanopyrrolo[1,2‐d][1,4]diazocines (I) based in the acidic cyclization of 2‐(1‐pyrrolylmethyl)tetrahydropyridines are described. In the first synthetic route, lithium aluminum hydride reduction of 2‐cyano‐1,4‐dimethyl‐1,2,3,6‐tetrahydropyridine (IIa) followed by reaction of the resulting primary amine with 2,5‐diethoxytetrahydrofuran affords the requisite tetrahydropyridine IVa. An analogous sequence from 2‐cyano‐4,6‐di‐methylpyridine (V) leads to the corresponding 2‐(1‐pyrrolylmethyl)pyridine VII which by quaternization and borohydride reduction yields a mixture of isomeric tetrahydropyridines, precursors of the pyrrolodiazocine systems Ib and Ic. Structural and stereochemical assignment of the synthesized compounds are discussed.