1H NMR sulfinyl group substituent effects of dithiinodiazine S-oxides as a key for structure assignment of parent dithiinodiazines

1,4-Dithiinodipyridine 1 was prepared by reduction of 4-chloro-3-chlorosulfonylopyridine (8) with HI/H(3)PO(3) system. Sulfur-assisted thermal isomerization of 1 resulted in a mixture of 1 and 2. Treatment of dithiinodiazines 1, 2, 5, and 6 with a nitrating mixture led almost selectively to respective S-monooxides 1a, 2a, 5a, and 6a. Due to the significant values of sulfinyl group substituent effects, (1)H NMR spectra of 1,4-dithiino-S-oxides 1a, 2a, 5a, and 6a permitted for structure assignment of parent dithiins 1, 2, 5, and 6 and confirmed regioselectivity of the reaction of dithiins 1, 2, 5, and 6 with nitrating mixture.