Hydroxyalkylpyrazines

Note The formation of alkyl- and hydroxyalkylpyrazines from glucose or glyc-eraldehyde and ammonium hydroxide at 150°C has been studied.1425... 

The general term oxypyrazine is used here to include derivatives such as the cy-cloamidic tautomeric pyrazinones (1), the alcoholic hydroxyalkylpyrazines (2), the etherial alkoxypyrazines (3-5), the cycloamidic nontautomeric pyrazinones (6), and pyrazine A-oxides (7, 8) in addition, related types like diketopiperazines, acy-loxypyrazines, pyrazine quinones, and endoperoxypyrazines are covered as appropriate. Some brief ancillary information on trivial names, natural occurrence, and biological activities of pyrazines (mainly oxy derivatives) is collected in a final Appendix section. 

These pyrazine ethers, both nuclear and extranuclear, undergo several useful reactions. Their hydrolysis to tautomeric pyrazinones or hydroxyalkylpyrazines has been covered in Sections 5.1.1 and 5.2.1. Other reactions are illustrated in the following examples ... 

Reactions of pyrazinecarbaldehydes already discussed include reduction to hydroxyalkylpyrazines (Section 5.2.1) and oxidation to pyrazinecarboxylic acids (Section 8.1.1) no Cannizzaro disproportionations appear to have been reported recently. 

Several major routes to pyrazine ketones have been covered already by primary synthesis in Chapters 1 and 2, by oxidation of aralkylpyrazines in Section 3.2.4.1, by oxidation of secondary hydroxyalkylpyrazines in Section 5.2.2, from pyrazinecarboxylic esters by the Claisen reaction in Section 8.2.2, from pyrazinecarbonyl halides (using several methods) in Section 8.3.2, and frompyrazinecarbonitriles with a Grignard (or similar reagent) in Section 8.6.2. 

The oxidation of alkyl-, styryl-, and hydroxyalkylpyrazines to carboxypyrazines mostly with potassium permanganate in aqueous solution but also with selenious acid in pyridine (669), selenium dioxide (676), and sodium dichromate in aqueous phosphoric acid (677) or acetic acid (678) have been described in Section IV.2C(1), and additional data are given below. 

Several important preparative routes to pyrazinecarboxylic acids have been discussed already by primary synthesis (Chapters 1 and 2), by oxidation of alkylpyrazines (Section 3.2.4.1), by the indirect ( ) oxidation of halogenoalkylpyrazines (end of Section 4.4), and by oxidation of hydroxyalkylpyrazines (Section 5.2.2). The remaining methods of preparation are indicated in the foUowing classified examples ... 

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