88381-44-6Relevant articles and documents
Spectroscopic and theoretical investigation of the conformational space of a pyrazolo-thiazole precursor of extended dipole diazafulvenium methide intermediates
Nunes, Cláudio M.,Lopes, Susy,Pinho e Melo, Teresa M.V.D.,Fausto, Rui
scheme or table, p. 101 - 108 (2009/08/15)
The structure, preferred conformers and vibrational spectra of the pyrazolo-thiazole precursor of extended dipole diazafulvenium methide intermediates, dimethyl 2,2-dioxo-1H,3H-pyrazolo[1,5-c][1,3]thiazole-6,7-dicarboxylate (DPTD) were investigated in low-temperature noble gas matrices (Ar, Xe), low temperature neat amorphous and crystalline phases and in KBr pellet (crystal and melted phases) by infrared spectroscopy, supported by quantum chemical calculations. Two types of conformers were observed spectroscopically in the matrices and in the neat amorphous solid resulting from fast condensation of the vapour of the compound onto the cold (20 K) substrate of the cryostat. These conformers correspond to the two pairs of nearly degenerated structures exhibiting skew/cis (conformers S′C and SC′) and gauche/trans (conformers G′T and GT′) arrangements of the N{double bond, long}C-C{double bond, long}O/C{double bond, long}C-C{double bond, long}O moieties. In the crystalline phase, the vibrational signature of the compound indicates that it exists in a skew/cis arrangement. After melting of the crystal, a conformational mixture is formed, where both skew/cis and gauche/trans forms exist in equilibrium and, with all probability, also conformer G′C′. This latter conformer cannot exist in the low temperature matrices and amorphous state, in view of the very low energy barrier that separates this form from the lower energy SC′ conformer, which can be easily surpassed during deposition of the compound (conformational cooling).
Azafulvenium methides: New extended dipolar systems
Sutcliffe, Oliver B.,Storr, Richard C.,Gilchrist, Thomas L.,Rafferty, Paul,Crew, Andrew P. A.
, p. 675 - 676 (2007/10/03)
The transient 8π 1,7-dipolar azafulvenium methides 5 and 8 undergo sigmatropic [1,8] H shifts and the acyl derivatives 12 electrocyclise to give novel pyrrolooxazines 13; the related diazafulvenium methide 15 can be intercepted in 8π + 2π cycloadditions with silylated acetylenes.
Kinetics and Mechanism of the Nitrosation of Thioproline: Evidence of the Existence of Two Reaction Paths
Castro, Albino,Iglesias, Emilia,Leis, Ramon J.,Tato, Jose Vazquez,Meijide, Francisco,Pena, M. Elena
, p. 651 - 656 (2007/10/02)
The kinetics of N-nitrosation of thioproline have been studied under a variety of experimental conditions.The experimental rate equation obtained in the absence of nucleophiles suggests that under these conditions nitrosation initially takes place at the sulphur atom, the nitroso group subsequently being transferred to the nitrogen atom.The fact that a primary isotope effect and general base catalysis are observed, together with the experimental rate equation, implies that the rearrangement is intramolecular, and that the rate-controlling step is the loss of a proton from the nitrogen atom of the S-nitrosated intermediate.Cl-, Br-, SCN-, and thiourea all catalyse the reaction via the formation of the corresponding nitrosyl compounds, which react directly with the unprotonated thioproline nitrogen atom in both the negatively charged and neutral forms of the amino acid.The observed rate constants for these reactions are discussed in terms of the nature of the nitrosating agent and the substrate.In the case of Br- and Cl- the plot of reaction rate against concentration of catalyst levels off at high values of the latter, showing that the protonated N-nitrosamine intermediate is in the steady state.The characteristics of the curve, which provide a measure of the susceptibility of the nitrosamine to nucleophiles, show that this is much less than that of aromatic amines of similar basicity.
