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.
- SourceAvailable from: Curt WentrupCurrent Organic Chemistry 09/2010; DOI:10.2174/138527210793563279 · 2.54 Impact Factor
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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: Multiphoton infrared absorption from a focused, pulsed CO(2) laser was used to initiate gas-phase thermal reactions of cis- and trans-3-penten-2-yl acetate. By varying the helium buffer gas pressure, it was possible to deduce the product distribution from the initial unimolecular reactions, separate from secondary reactions in a thermal cascade. Thus, trans-3-penten-2-yl acetate gives 54 +/- 5% of beta-elimination to give trans-1,3-pentadiene, 40 +/- 3% of [3,3]-sigmatropic rearrangement to give cis-3-penten-2-yl acetate and 6 +/- 4% of cis-1,3-pentadiene. Similar irradiation of cis-3-penten-2-yl acetate gives 45 +/- 1% of beta-elimination to give cis-1,3-pentadiene, 32 +/- 2% of [3,3]-sigmatropic rearrangement to give trans-3-penten-2-yl acetate and 23 +/- 2% of trans-1,3-pentadiene. The latter process is an eight-centered delta-elimination, which is argued to be a pseudopericyclic reaction. Although beta-eliminations have been suggested to be pericyclic, B3LYP/6-31G(d,p), MP2 and MP4 calculations suggest that both beta- and delta-eliminations, as well as [3,3]-sigmatropic rearrangements of esters are primarily pseudopericyclic in character, as judged by both geometrical, energetic and transition state aromaticity (NICS) criteria. Small distortions from the ideal pseudopericyclic geometries are argued to reflect small pericyclic contributions. It is further argued that when both pericyclic and pseudopericyclic orbital topologies are allowed and geometrically feasible, the calculated transition state may be the result of proportional mixing of the two states; this offers an explanation of the range of pseudopericyclic and pericyclic characters found in related reactions.Journal of the American Chemical Society 02/2009; 131(2):528-37. DOI:10.1021/ja804812c · 11.44 Impact Factor