Carbinols from Aldol-Type Condensations

Tetramethylpyrazine, p-dimethylaminobenzaldehyde, and 37% hydrochloric acid have been shown to give 2,3,5,6-tetra(p-dimethylaminostyryl)pyrazine (713). Similar condensations have also been applied to quarternary salts ofmethylpyrazines with a piperidine catalyst (714). Thus 1,2,5-trimethylpyrazinium methylsulfate and benzaldehyde gave 1,5-dimethyl-2-styrylpyrazinium methylsulfate. 

In the pyrazine series, the Mannich reaction was applied first to 2,5-dimethyl-pyrazine by Linder and Spoerri (715). Of the amines tried, positive reactions were obtained only with dime thy lamine, piperidine, and morpholine, and it was found that one, or more usually two, of the hydrogen atoms of each of the methyl groups could be substituted. Thus 2,5-dimethylpyrazine, dimethylamine hydrochloride, and formalin in refluxing isopentyl alcohol gave 2,5-bis[bis(dimethylaminomethyl)-methyl]pyrazine and 2,5-bis(j3-dimethylaminoethyl)pyrazine. Reaction of 2-methyl-pyrazine with formalin and diethylamine hydrochloride gave 2- 3-diethylamino-ethylpyrazine (716) similarly dimethylamine hydrochloride gave 2-dimethyl-aminoethylpyrazine (17) and some 2-[bis(dimethylaminomethyl)]methylpyrazine (18) (657). 

Condensation of 2-methylpyrazine with the Vilsmeier reagent, phosphoryl chloride, and dimethylformamide gave 2-(2 -dimethylamino-r-formylvinyl)pyTazine (19) (717). 

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