(A) new synthesis and mass spectral fragmentation behavior of alkoxy-substituted N-alkyl-1,3,4(2H)-isoquinolinetriones

Abstract

A new method was investigated for synthesis of alkoxy-substituted N-alkyl-1,3,4(2H)-isoquinolinetriones using ring closure reactions of Pomeranz-Fritsch reactions and Bobbitt``s modification. The reaction of oxalyl chloride with the secondary benzamides in an appropriate solvent at 60℃ gave N-aroyloxamoyl chlorides. These isolable intermediates underwent cyclization on raising the reaction temperature. The reactivity was enhanced in more polar solvent and the ortho: para isomer ratio of alkoxy-substituted N-alkyl-1,3,4(2H)-isoquinolinetriones was increased when the solvent, decaline, was changed to sulfolane. The synthesized compounds were characterized by IR, $^1H$ NMR, UV and mass spectrometry, and the spectroscopic data of the compounds were discussed to elucidate their structure. The mass spectra of a series of alkoxy-substituted N-alkyl-1,3,4(2H)-isoquinolinetriones at 70 eV were obtained and the similarities and differences of their characteristic fragmentations were investigated. Primary main degradation reactions of these compounds occurred by cleavage of the amide bond, followed by the elimination of carbon monoxide. In general, the ions resulted after elimination of carbon monoxide appeared to undergo fragmentation by two major pathways; one was characterized by loss of HC(=O)N=$CHR_1$ via a hydrogen transfer, and it was found that the latter route was predominant judging from the relative intensities of the respective ions.