Thianthrene 5-oxides synthesis

The direct synthesis of fully functionalized sugars possessing amino or hydroxyl functions at C-2 has also been studied. Thus, activation of glycals by thianthrene-5-oxide 287 and Tf20, followed by treatment with an amide nucleophile and a glycosyl acceptor, led directly to various 2-acylamido glycosides 288 [610,611] (Scheme 4.59). 

The synthesis of 5-arylthianthrenium salts, 8, [CRI 02a, CRI 04] can be carried out by the condensation of thianthrene-S-oxide with various aromatic compounds bearing electron-donating substituents, R, as depicted in equation [2.1], A mixture of methanesulfonic acid and phosphorous pentoxide serves as an acid catalyst and dehydrating agent for this reaction. Replacement of the methanesulfonate anion by a metathetical reaction with NaMtXn affords the desired active photoinitiator, 8. Depending on the specific R substituent, 5-arylthianthrenium photoinitiators have UV absorption maxima in the range of 300-400 nm. 

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