Lead tetra-acetate oxidation of tetrahydrobenzazepine enamides: the synthesis of N-acyl substituted tetrahydro-3-benzazocin-2(1H)-ones. A chemical and crystallographic study

Abstract

Oxidation with lead tetra-acetate of various N-acetyl, N-benzoyl and N-alkoxycarbonyl enamides derived from dihydrobenzazepines leads to a convenient synthesis of N-acyltetrahydrobenzazocinones. Unexpected rate decreases were observed for the N-acetyl and N-benzoyl derivatives with 7,8,9-trimethoxy substitution. Based on crystallographic analysis, these are attributed to conformational effects determining the extent of double bond conjugation with the aromatic ring and, primarily, the nitrogen lone pair. A comparison of oxidation and subsequent cleavage of the various N-alkoxycarbonyltetra-hydrobenzazocinones demonstrated that the N-t-butoxycarbonyl group gives the highest overall yield of the tetrahydrobenzazocinone from the dihydrobenzazepine.