Celia B. Schapira

Improved Synthesis of N-Substituted 2,3-Pyridinedicarboximides with Microwave Irradiation

The microwave-induced synthesis of N-substituted 2,3-pyridinedicarboximides (1) by means of two different approaches is presented. One involves direct N-alkylation of quinolinimide (2) (Method A) and the other, dehydrative condensation of quinolinic anhydride (4) and amines (Method B). Reactions resulted highly accelerated, with improved yields in relation to those obtained by conventional heating. The scope and limitations of each method and its variants are discussed.

Spectroscopic and theoretical studies of derivatives of 1,6- and 1,7-naphthyridines.

The solvatochromism in 8-hydroxy-1,6-naphthyridin-5(6H)-one-7-carboxylic acid methyl ester (1), 5-hydroxy-1,7-naphthyridin-8(7H)-one-6-carboxylic acid methyl ester (2), and 4-hydroxy-2-methyl-1(2H)-isoquinolone-3-carboxylic acid methyl ester (3), has been studied in solvents of different polarity and hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) ability. The relative stabilities of isomers for these naphthyridine derivatives and their interaction with the solvent are reported. Two intramolecular hydrogen-bonded structures contribute to the ground state of compound 1. Temperature effects on the absorption bands were recorded to analyse the possible equilibrium between covalent and zwitterionic forms. The formation of zwitterionic species was observed only in HBD solvents, from which is inferred the solvent assistance in the proton transference. AM1 and PM3 semi-empirical calculations were used in support of the proposed interpretations.

Identification and characterization of 4-hydroxy-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxide derivatives by mass spectroscopy

Abstract Electron impact mass spectral fragmentation of certain esters and amides derived from 4-hydroxy-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxide is described. Common ions to both series may be observed, as well as others allowing them to be differentiated. The method is promissory for identification and analysis of these compounds.

Decarboxylation of 4-Hydroxy-2H-1,2-Benzothiazine-3-carboxylic Acid 1,1-Dioxide 13C NMR Detection of an Enolic Intermediate

An intermediate compound, most likely enolic (A), was detected by 13 C-NMR spectroscopy during decarboxylation of 4-hydroxy-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxide (I)