Dimethyl ammonium perchlorate, reaction with

Dimethyl-2,4-diphenyl-3-azapyrylium perchlorate 381 is converted under the Vilsmeier-Haack reaction conditions into the N,jV-dimethylaminovinyl derivative 382. By refluxing 382 in acetic acid mixed with either ammonium acetate or / -toluidine, compound 383 was obtained by an unusual recyclization via elimination of the iV,A-dimethylaminovinyl group (equation 109). 

To a flask equipped with a condenser were added 70 g 2-methyl-5-methoxy y-pyrone (0.2 mol) and 31 g dimethyl sulfate (0.25 mol). The mixture was heated at 50°C for 2 h, and was then poured into 3 eq. of ice-cooled 20% HCIO4. After 2 h, the pyronium perchlorate salt was filtered and added to 175 mL 10% ammonium carbonate solution saturated with ammonium sulfate. After the reaction, the product was extracted with EtOAc. The product was obtained via evaporation of solvent and vacuum distillation, b.p. 75-80° C (1 mmHg). The product can also be converted to hydrochloride salt, m.p. 164°C. 

In 1910, Adolf von Baeyer at the University of Munich reported that the product from the reaction of dimethylsulfate and 2,6-dimethyl-4//-pyran-4-one 4 at 50 °C formed an insoluble pyrylium salt 5 when treated with perchloric acid. Treatment of the isolated solid with aqueous ammonium carbonate generated 4-methoxy-2,6-dimethylpyridine (6). 

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