Synthesis and reactions of cyclic isoimidium salts

Abstract

Treatment of secondary and tetriary succinamic acids with acetic anhydride and perchloric acid gave succinisoimidium perchlorates (5), which reacted with primary and secondary amines to yield NN′-substituted succinamides. The deprotonation of tertiary and secondary succinisoimidium salts was investigated and evidence for the formation of unstable N-phenyl- and N-t-butyl-succinisoimides was obtained. Six phthalisoimidium perchlorates (11) were prepared; their reactions with nucleophiles are described. Stable phthalisoimides, obtained from secondary phthalisoimidium perchlorates, were studied. In the homophthalic acid series, five 3-ammonio-3,4-dihydro-1H-2-benzopyran-1-one perchlorates (27) were prepared, which yielded N-substituted 3-amino-1H-2-benzopyran-1-ones (28) on deprotonation. An isomeric homophthalisoimidium salt, 3,4-dihydro-1-morpholinio-1H-2-benzopyran-3-one perchlorate (32), was synthesised. Isoimidium salts derived from αα′-diphenylsuccinic, maleic, cyclopropane-1,2-dicarboxylic, and diphenic acid were obtained. 1,2-Dihydro-2-dimethylammonio-3,1-benzoxazin-4-one perchlorate (47) was converted into 2-dimethylamino-3,1-benzoxazin-4-one (48).