Unexpected formation of N-(1-(2-aryl-hydrazono)isoindolin-2-yl)benzamides and their conversion into 1,2-(bis-1,3,4-oxadiazol-2-yl)benzenes.

Reaction between ortho-phthalaldehyde and various aroylhydrazines unexpectedly yields N-(1-(2-aryl-hydrazono)isoindolin-2-yl)benzamides as major products along with the predictable 1,2-bis-aroylhydrazones. NMR investigation of the major reaction products indicate the presence of a mixture of geometrical isomers, in various ratios. Single crystal X-ray diffraction confirms the proposed structure and indicates a Z configuration of the C═N double bond substitutents. Optimization of the condensation reaction conditions enabled quantitative isolation of the cyclic isomer. Oxidation of the isomers with bis(trifluoroacetoxy)iodobenzene (PIFA) leads to rapid formation of new highly fluorescent 1,2-bis(5-aryl-1,3,4-oxadiazol-2-yl)benzenes.