A computational study of the formation and dimerization of benzothiet-2-one
ABSTRACT A computational B3LYP/6-31G(d,p) study of the formation of benzothiet-2-one (4) from benzothiophenedione (2) and its subsequent dimerization to 5 was performed. The proposed intermediate ketene 3 has no gas-phase barrier to ring closure to 4. Three transition structures for dimerization were located. The geometry of the lowest energy one (TS8a) has a geometry corresponding to a two atom + two atom, face-to-face addition of the two thiolactone moieties. The orbital interactions suggest that the reaction is pseudopericyclic.
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ABSTRACT: This report surveys the 2007 literature on mechanisms of pericyclic reac-tions. One recurring theme in this year's reports is catalysis. Several studies addressed the catalysis of cycloaddition reactions by preorganization (via encapsulation, hydrogen bond directed precomplex formation, or hydro-phobic effects) or selective transition state stabilization (via hydrogen bonding interactions) and the acceleration of sigmatropic shifts by selective transition state stabilization (via hydrogen bonding, transition metal com-plexation, and weak interactions with halogens) or addition of an electron. In addition, the mechanisms of several interesting cascades consisting of multiple types of pericyclic reactions linked in tandem were examined in detail.ChemInform 12/2007; 38(52). DOI:10.1002/chin.200752273
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ABSTRACT: Reaction of 3-alkylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles with maleimides, dimethyl maleate and dimethylacetylene dicarboxylate were carried out to give octahydro-pyrrolo[3,4-alpha]pyrrolizin-4-ylidenes, hexahydro-pyrrolizines and 6,7-dihydro-5H-pyrrolizines. The formation of the synthesized compounds is explained by a 1,3-dipolar cycloaddition of an in situ generated azomethine ylide. The mechanisms of the formation of these active intermediates were discussed with the aid of density functional theory methods with the B3LYP functional 6-31G(+) calculations using the STAN method and chemical experiments.Tetrahedron 09/2009; 65(36-36):7662-7672. DOI:10.1016/j.tet.2009.06.114 · 2.82 Impact Factor
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ABSTRACT: Flash vacuum pyrolysis studies of substituted 6-acetoxy-2,4-cyclohexadienones (3 and 10) from 300 °C to 500 °C provide strong experimental evidence that direct [3,5]-sigmatropic rearrangements in these molecules are favored over the more familiar [3,3]-rearrangements. The preference holds when the results are extrapolated to 0.0% conversion, indicating that this is a concerted process. Pyrolysis of 6,6-diacetoxy-2-methyl-2,4-cyclohexadienone (9) at 350 °C gives a modest yield of the initial [3,5]-rearrangement product, 2,6-diacetoxy-6-methyl-2,4-cyclohexadienone (11). Qualitative arguments and electronic structure theory calculations are in agreement that the lowest energy pathway for each [3,5]-rearrangement is via an allowed, concerted pseudopericyclic transition state. The crystal structures of 3, 9, and 10 prefigure these transition states. The selectivity for the [3,5]-products increases with increasing temperature. This unexpected selectivity is explained by a concerted, intramolecular, and pseudopericyclic transition state (TS-5) that forms a tetrahedral interemediate (ortho-acid ester 4´), followed by similar ring openings to isomeric phenols, that shifts the equilibrium towards the phenols from the [3,5]- (but not the [3,3]-) products.Journal of the American Chemical Society 08/2013; 135(38). DOI:10.1021/ja4077364 · 11.44 Impact Factor