A new thiatriazine isomer: Synthesis, tautomerism, and molecular structure of 3,6-diphenyl-4H-1,2,4,5-thiatriazine as a precursor to the 1,2,4,5-thiatriazinyl radical

John M. Farrar, Mahesh K. Patel, Piotr Kaszynski, Victor G. Young

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Abstract

The diphenyl derivative of 4H-1,2,4,5-thiatriazine (5) was prepared by oxidative cyclization of 9. The molecular structure of 5, obtained by X-ray diffraction [orthorhombic, Pna21, a = 9.7746(13) Å, b = 21.692(2) Å, c = 5.6580(8) Å, compares favorably with that predicted with ab initio calculations. The thiatriazine 5 was used as a precursor to the 3,6-diphenyl- 1,2,4,5-thiatriazinyl radical (4) through either oxidation with PbO2, or conversion to and reduction of sulfiminyl chloride 6 with Ph3Sb. The weak ESR quintet (a(N) = 1.03 mT, g = 2.0103) observed in the latter case correlates well with the molecular structure of 4, but the results of DFT calculations are ambiguous. Ab initio calculations show that 4H-1,2,4,5- thiatriazine (I-4H) is the most stable tautomer and is the second most stable isomer among the six possible thiatriazines. All isomeric thiatriazinyl radicals exhibit similar spin distribution patterns. 1,2,4,5-Thiatriazinyl radical (I-R) is calculated to be 23.1 kcal/mol less stable than the most stable 1,2,4,6 isomer II-R.

Original languageEnglish (US)
Pages (from-to)931-940
Number of pages10
JournalJournal of Organic Chemistry
Volume65
Issue number4
DOIs
StatePublished - Feb 25 2000

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