An exploration of the cycloaddition and oxidative dehydrogenation chemistry of SNS+ with 1,4-quinone derivatives and characterization of the corresponding hybrid quinone-thiazyl cations and radicals

The development of new and convenient synthetic routes to SNS + as the SbF6- salt from readily available starting materials has lead to the continued exploration of the versatile cycloaddition chemistry of SNS+. The cycloaddition chemistry of SNSMF6 (M = As, Sb) was successfully extended to the simple cross-conjugated 1,4-benzoquinone leading to the hydroquinone fused 1,3,2-dithiazolylium cation, as the MF6- salts in essentially quantitative yield. The hydroquinone fused 1,3,2-dithiazolylium derivative is a unique example of a thiazyl cation in the presence of both potentially labile and reactive hydroxyl functionalities that was subsequently oxidized to the 1,4benzoquinone fused 1,3,2-dithiazolylium cation by AsF5 in the presence of triethylamine (NEt3) in high yield. The combined oxidative dehydrogenation and cycloaddition chemistry of SNS+ with the hydroquinone fused 1,3,2-dithiazolylium cation in refluxing liquid SO2 led to the 1,4-benzoquinone bridged bis-1,3,2-dithiazolylium dication in moderate yield (ca. 60-65 %). Similarly, the 'one-pot' oxidative dehydrogenation and cycloaddition chemistry of SNS+ with 1,4-naphthaquinone under mild conditions led to the 1,4-naphthoquinone fused 1,3,2-dithiazolylium cation in high yield (ca. 87 %).;The reduction of the hydroquinone and quinone fused 1,3,2-dithiazolylium cations led to the expected 1,3,2-dithiazolyl radicals in solution, which were characterized by EPR. In contrast, the one electron reduction of the benzoquinone-bridged bis-1,3,2-dithiazolylium dication led to a unique zwitterionic semiquinone radical-cation. The 1,4-naphthaquinone fused 1,3,2-dithiazolyl radical is the first example of an isolable hybrid quinone-thiazyl radical and its full characterisation in the solid state is reported. The thermal decomposition of this radical (in vacuo) led to a novel 1,4-naphthaquinone fused polysulfane and a known 1,2,5-thiadiazole derivative.;The regio-selective cycloaddition of SNSSbF6 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in a 2:1 molar ratio in liquid SO2 led to the dicycloaddition of SNS+ exclusively at the nitrile functionality despite the presence of other potentially reactive unsaturated centers. In contrast, the cycloaddition of SNS+ as the Al(OC(CF3)3) 4- salt with DDQ led only to the monocycloaddition product, as identified by multinuclear NMR. The general thermodynamic trends for the cycloaddition chemistry of SNS+ as the MF6- and Al(OC(CF3)3)4- salts with multifunctional nitriles were established in all three phases by simple thermodynamic models based on DFT calculations and the volume-based thermodynamic (VBT) approach.