- Gas-phase reactivity of protonated 2-oxazoline derivatives: Mass spectrometry and computational studies
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RATIONALE Oxazolines have attracted the attention of researchers worldwide due to their versatility as carboxylic acid protecting groups, chiral auxiliaries, and ligands for asymmetric catalysis. Electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis of five 2-oxazoline derivatives has been conducted, in order to understand the influence of the side chain on the gas-phase dissociation of these protonated compounds under collision-induced dissociation (CID) conditions. METHODS Mass spectrometric analyses were conducted in a quadrupole time-of-flight (Q-TOF) spectrometer fitted with electrospray ionization source. Protonation sites have been proposed on the basis of the gas-phase basicity, proton affinity, atomic charges, and a molecular electrostatic potential map obtained on the basis of the quantum chemistry calculations at the B3LYP/6-31 + G(d,p) and G2(MP2) levels. RESULTS Analysis of the atomic charges, gas-phase basicity and proton affinities values indicates that the nitrogen atom is a possible proton acceptor site. On the basis of these results, two main fragmentation processes have been suggested: one taking place via neutral elimination of the oxazoline moiety (99 u) and another occurring by sequential elimination of neutral fragments with 72 u and 27 u. These processes should lead to formation of R+. CONCLUSIONS The ESI-MS/MS experiments have shown that the side chain could affect the dissociation mechanism of protonated 2-oxazoline derivatives. For the compound that exhibits a hydroxyl at the lateral chain, water loss has been suggested to happen through an E2-type elimination, in an exothermic step.
- Vessecchi, Ricardo,Tomaz, Jose Carlos,Santos, Guilherme Purcote Dos,De Oliveira, Alfredo R. Marques,Lopes, Norberto Peporine,Clososki, Giuliano Cesar
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experimental part
p. 1061 - 1069
(2012/08/08)
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- Condensed oxaziridine-mediated [3+2] cycloaddition: Synthesis of polyhetero-bicyclo compounds
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Polyhetero-bicyclo compounds were synthesized by a regioselective [3+2]-cycloaddition reaction between stable condensed oxaziridines and alkenes, alkynes, and nitriles. These molecules showed considerable antimicrobial activity against several gram-positive bacteria.
- Videtta, Valeria,Perrone, Serena,Rosato, Francesca,Alifano, Pietro,Tredici, Salvatore M.,Troisi, Luigino
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scheme or table
p. 2781 - 2783
(2010/12/25)
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- Generation of cyclic ketene-N,X-acetals (X = O, S) from 2-alkyl-1,3-oxazolines and 2-alkyl-1,3-thiazolines. Reactions with acid chlorides, 1,3-diacid chlorides and N-(chlorocarbonyl) isocyanate
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2-Alkyl-1,3-oxazolines, 2-alkyl-1,3-thiazolines, and the corresponding cyclic ketene-N,X-acetals (X = O, S) derived from them were reacted with monoacid chlorides, diacid chlorides, triacid chlorides. A series of these carbon-carbon bond-forming reactions and cyclizations to both substituted 2,3-dihydrooxazolo[3,2-a]pyridine-5,7-diones and 2,3-dihydrothiazolo[3,2-a] pyridine-5,7-diones proceeded under mild reaction conditions. Cyclic ketene-N,X-acetal intermediates play important roles in all these reactions. Related cyclizations with N-(chlorocarbonyl) isocyanate formed substituted 2,3-dihydrooxazolo[3,2-c]pyrimidine-5,7-diones and 2,3-dihydrothiazolo[3,2-c] pyrimidine-5,7-diones. Georg Thieme Verlag Stuttgart.
- Zhou, Aihua,Pittman Jr., Charles U.
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- SYNTHESIS OF ISOTHIOCYANATES FROM NON-AROMATIC NITROGEN-CONTAINING HETEROCYCLES
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Investigation of the reaction of thiophosgene with Δ2-oxazolines I, Δ3-thiazolines II, 4H-benzothiazines III, 2-methoxypentahydro-Δ1-azepine IV, theophylline and caffeine showed that only compounds I and IV reacted to give 2-acyloxyethyl isothiocyanates and methyl 6-isothiocyanatohexanoate.The structure of these products was corroborated by IR, 1H NMR, 13C NMR and mass spectral methods.The suitability of the above-mentioned compounds to react is discussed.
- Gonda, Jozef,Kristian, Pavol,Mikler, Lubomir
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p. 112 - 117
(2007/10/02)
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