Synthesis and molecular structure of 2,3,4,5-tetrahydro-1H-3-benzazepine derivatives and dimethyl 4-cyano-2,3,6,7-tetrahydro-1H-3-benzazonine-5,6-dicarboxylate

A study was carried out on the direction of 1,2,3,4-tetrahydroisoquinolinium quaternary salt rearrangements by the action of base with or without dimethyl acetylenedicarboxylate. These quaternary salts containing a methylene group at the nitrogen atom, are converted in the presence of base through intermediate N-ylides into the Stevens rearrangement products, namely, tetrahydro-3-benzazepines. Upon the addition of dimethyl acetylenedicarboxylate as an electrophilic trap, this diester adds at the carbanion site of the ylide with subsequent recyclization of the piperidine fragment to give a 2-benzazonine derivative with an unusual 4,5-positioning of the olefin bond in the nine-membered heterocycle. An X-ray structural analysis established the molecular structures of 2-cyano-3-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine and dimethyl 4-cyano-2,3,6,7-tetrahydro-1H-3-benzazo-nine-5,6-dicarboxylate.