Vinylpyridines sulphurous acid

Treatment of the alcohol derived from 3-methyltriazolpyridine 72 with aqueous sulphuric acid gave the alcohol 78 (60%) as a diaster-eoisomeric mixture, d.e. 5% (determined by NMR), and with acetic acid, acetate 80 (75%, d.e. 5%) was obtained. The chiral fenchyl group is too far from the triazolopyridine 3-position for chiral induction. In both cases small quantities of the elimination product, vinylpyridine 79, is formed. Under the usual conditions for treatment with selenium dioxide (i.e. 2,5M sulphuric acid, 80 °C, 24 h) (85JP12719) no reaction was observed. However, in p-xylene at reflux temperature, known pyridine 81 was obtained (97TA1869), probably due to a total oxidation followed by decarboxylation of the first-formed ketone 82 (Scheme 16). 

The triazol ring-opening reaction of the sulphoxides 97, 101 and 103 gave 2-sulphinylp5uidines, previously unknown. These reactions were performed with acetic acid or sulphuric acid as electrophiles. Treatment of 97 with aqueous sulphuric add gave alcohol 107 (95%) as a diastereoi-someric mixture, 5% d.e. (determined by NMR), and with acetic add the acetate 108 (89%, 7% d.e.) was obtained. Small quantities of the elimination product, the vinylpyridine 109 were also formed (Scheme 22). 

The expected sulphonic acids are formed by addition of sulphurous acid to 2- and 4- but not 3-vinylpyridine337/ 347e and C-S bonds have also been formed by additon of hydrogen sulphide ss, thiols358-9a, 360 sulphinic acids , thioacids and thiourea (with which 2-methyl-5-vinylpyridine did not react). 

There have been several reports on oxidation reactions by copper(ii)-poly(4-vinylpyridine) complexes such as those of L-ascorbic acid, oxyanions of sulphur, phenol derivatives, and the dimerization of acetylenes. ... 

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