Thianthrenes proton

In 1,1,2,2-tetrachlorethane solution, the spectra of thianthrene and trans-thianthrene 5,10-dioxide are temperature independent for the cis-isomer, the lower-field resonance shifts further downfield with increasing temperature while the signals for 2-, 3-, 7-, and 8- protons remain constant over a 200° range. In chloroform, small, apparant temperature-dependent shifts for thianthrene, at all positions, were attributed to temperature-dependent shifts of the reference solvent signal. Using this, it was shown... 

In 5-alkylthianthrenium salts, the 4- and 6-proton signals are pulled downfield by 0.5-0.9 ppm, and in 5-arylthianthrenium salts, the signals are pulled downfield by 0.4-0.8 ppm. These peri protons are downfield by ----47 ppm with respect to CHCI3 in thianthrene sulfoxides. 

Thianthrene 5-oxide is converted, in concentrated sulfuric acid, into a solution of T (62JA4798) sulfuric or perchloric acid in nitromethane can also be used (63TL993). One view is that this transformation involves homolysis of the O-protonated sulfoxide, with hydroxyl radical as byproduct, though the involvement of a dication has also been suggested (63JOC2828). 

Attempted displacement of thianthrene from 37 (R = Et02C, R = Me), using sodium 4-methylbenzenesulfinate, caused deacetylation to yield ylid 38 (R = H, R = OEt). It was shown that this was C-protonated to afford the thianthrenium salt 37 (R = H, R = OEt) upon treatment with acid. 

The proton spectra for the dibenzo derivatives, viz. dibenzo[6,e][l,4]dioxin, phenoxathiin and thianthrene, have been reported in full, as part of a wider survey of heterocyclic compounds structurally related to anthracene. The protons in dibenzo[6,e ][ 1,4]dioxin are the most shielded, and in phenoxathiin the protons ortho and para oriented to the C—O bond are shielded relative to those ortho and para to sulfur <740MR(6)U5). The 13C chemical shifts for phenoxathiin follow a similar pattern, with carbons ortho and para to the C—O bond resonating at 117.5 and 124.2 p.p.m. respectively, and at higher field than those ortho, para to the C—S bond (127.4 and 126.5 p.p.m.), in good agreement with shifts predicted on the basis of additivity effects <73JMR(12)143). 

Dibenzo[6,e][l,4]dioxin, phenoxathiin and thianthrene all react with butyllithium with proton abstraction from a benzene ring. Dibenzo[f ,e][l,4]dioxin and thianthrene are metallated at the 1-position (128), while lithiation of phenoxathiin occurs ortho to the C—O bond rather than the C—S bond, i.e. at C-4, (129). The lithiated products provide excellent intermediates for functionalizing the rings at these positions, usefully complementing the product distribution pattern in electrophilic substitution reactions. 

For mesitylene and durene, the kinetics have been followed by specular reflectance spectroscopy [17]. The results indicated that mesitylene produces a fairly stable radical cation that dimerizes. That of durene, however, is less stable and loses a proton to form a benzyl radical, which subsequently leads to a diphenylmethane. The stability of the radical cation increases with increasing charge delocalization, blocking of reactive sites, and stabilization by specific functional groups (phenyl, alkoxy, and amino) [18]. The complex reaction mechanisms of radical cations and methods of their investigation have been reviewed in detail [19a]. Fast-scan cyclovoltammetry gave kinetic evidence for the reversible dimerization of the radical cations of thianthrene and the tetramethoxy derivative of it. Rate constants and enthalpy values are reported for this dimerization [19b]. 

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