Pyridinium disulfonates

Disulfonation can be achieved by treating furan with pyridinium-A -sulfonate in dichloromethane over several days (Scheme 6.24). 

The /V-(2,6-dimethy 1-4-oxopyridin-1 -yl)pyridinium salts (15)24 have proved to be versatile intermediates for the regiospecific synthesis of 4-substituted pyridines (17) via attack by the appropriate carbon nucleophiles, e.g. ionized ketones,90 nitroalkanes,91 esters and nitriles,92 and a-diketones, a-keto esters, a-diesters, disulfones etc. (Scheme 10).93 Aromatization of the intermediate 1,4-dihydro adduct (16) was generally achieved under free radical conditions. 

Definite sulfimide sulfonic acids are formed from S03 adducts and sulf-amide in a melt the pyrid nium salt of the sulfamide disulfonic acid, H0(02SNH)2—S03H was obtained. The analogous reaction with imido-sulfamide results in the dipyridinium salt of trisulfimide sulfonic acid H0(02SNH)3—S03H. Besides the pyridinium salts, several potassium, ammonium and sodium salts were prepared (92a). 

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