Cyclization of Nitriles by Halogen Acids. II. New Synthesis of Substituted 3H-Azepines

The treatment of 2-aryl-(or alkyl-) 1, 4-dicyano-1-butenes (III) having syn-nitrile groups with hydrogen bromide in anhydrous media leads to 2-amino-5-aryl-(or alkyl-) 7-bromo-3H-azepines in good yield. However, a new attempt to obtain the corresponding azepine from cls-1, 4-dieyano-l-butene was once again unsuccessful, despite the fact that 1, 4-dicyano-2-methylbutene-1 did give the expected azepine derivative. The dinitriles required for the cyclization studies were synthesized by conventional methods and their stereochemistry was assigned by comparing their nmr spectra with those of suitable model compounds. The previous geometrical assignments of the cis-and trans-1, 4-dicyano-1-butenes were found to be incorrect.