The gas-phase proton affinities of 3-thio-5-oxo, 5-thio-3-oxo, and 3,5-dithio derivatives of 2,7-dimethyl-[1,2,4]-triazepine have been measured by means of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The structures and vibrational frequencies of all the stable protonated tautomers and all the transition states connecting them have been obtained by means of the B3LYP density functional method, together with a 6-31G* basis set expansion. The final energies were obtained at the B3LYP/6-311+G(3df,-2p) level. In contrast with the results from the analogous thiouracils, our results indicate that all of these compounds behave as sulfur bases in the gas phase. For 5-thio-3-oxo-[1,2,4]-triazepine and 3,5-dithio-[1,2,4]triazepine, the thiol-enol and the dithiol forms are the most stable protonated species, respectively. Conversely, for 3-thio-5-oxo-[1,2,4]-triazepine, the thiol-ketone form is the most stable one. For 5-thio-3-oxo-[1,2,4]triazepine and 3,5-dithio-[1,2,4]-triazepine, as it was found for thiouracils, a comparison between theoretical and experimental proton affinities suggests the formation of dimers between protonated and neutral species, which favors proton-transfer mechanisms leading to the formation of the most stable protonated species.

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The condensation of mesitonitrile and dichlorocarbene in aqueous medium to 1,2,4--triazepines has been studied. In all cases this cycloaddition is peri and regiospecific. Compounds with the unknown ring systems isoxazolo[5,4-e]-l,2,4-triazepine and azirino[2,1-g]-1,2,4-triazepine have been synthesized. The structural elucidation of these products was accomplished by spectral evidences.Nous avons decrit recemment la synthese de la triazepine--1,2,4 1 ( Fig. 1) et montre qu'elle pouvait jouer le r6le de diene dans des cycloadditions [4 + 21 n vis a vis de differents dienophiles'. La reaction n'engageait que I'un des dienes potentiels, entre les atomes C-3 et C-6. Nous dtcrivons ici le comportement de 1 vis a vis d'un dip6le-1,3: I'oxyde de mesitonitrile* 2 et du dichlorocarbtne Abstract. The NADH models, (1 R)-1,4-dihydronicotinamide and (1 R)-I ,4-dihydroquinoline-3-carboxamide (1-4, R = X-benzyl or octyl), are readily oxidized by methylene blue (MB*), yielding the corresponding pyridinium ions and leuco-methylene blue (MBH). Under aerobic reaction conditions, molecular oxygen, present in the reaction solution, rapidly reoxidizes MBH to MB@, thereby allowing the study of the oxidation of the NADH models under pseudo-first-order reaction conditions. In order to elucidate the mechanism of the oxidation of the NADH models by MB*, the influence of the MB* concentration, solvent and temperature has been studied as well as the effect of substituent variation in the benzyl group in a series of I-(X-benzyl)-l,4-dihydronicotinamides (la-f). For one of the model compounds, 1 -benzyl-1,4-dihydronicotinamide (la, BNAH), the primary and the secondary isotope effect and the temperature dependence of the kinetic isotope effect have been determined. It is concluded that oxidation of the NADH models by MB* most likely proceeds by a rate-determining hydride transfer process via a linear, symmetrical transition-state structure.

Nous décrivons les réactions de cycloaddition de la diméthylthic‐3,5 triazépine‐1,2,4 1 avec différents diènophiles. La phényl‐4 triazoline‐1,2,4 dione‐3,5, le diméthylacétylène dicarboxylate, l'anhydride maléïque réagissent avec 1 selon une réaction [4 + 2]π. Excepté le premier, ces adduits subissent un réarrangement sigmatropique‐1,3 pour conduire aux hétérocycles.