Isolation and reaction of new aromatic dications. 4-Thioniapyridinium dications: 2-aryl-(or 2-alkyl-) 4-methyl-3-oxo-2H-1, 4-thiazin-2-ylium tetrafluoroborates
'H NMR chemical shifts for the cations 6 recorded in TFA as solvent are listed in Table 111. As is seen in Table 111, signals for the protons at the 5-position of cations 6 appeared in the range of 6 8.30 (R'= p-MeOC, H,) to 8.69 (R'= Ph) and showed large downfield shifts of 2.12 (R'= p-MeOC, H,) to 2.59 (R'= Ph) ppm compared to those of corresponding precursor keto alcohols 5. Large downfield shifts (1.9-2.4 ppm) can also be seen with the protons at the 6 ...
