Reduction of a-Hydroxyimino Carbonyl Compounds

This method of preparation (5 6 3), first discovered by Gutknecht (15,16), 

Other reducing conditions have also been widely used. Thus zinc and sodium hydroxide has been utilized for the conversion of 1-hydroxyimino-l-phenylacetone to 2,5-dimethyl-3,6-diphenylpyrazine (191) dithionite for the conversion of a-benzoyl a-hydroxyiminoacetanilide to 2,5-diphenyl-3,6-bis(7V-phenylcarbamoyl)-pyrazine (192) sodium amalgam for benzil monoxime to tetraphenylpyrazine (193) aluminum amalgam for hydroxyiminoacetoacetic ester to 2,5-bisethoxy-carbonyl-3,6-dimethylpyrazine (194) and sodium and alcohol for benzil dioxime to tetraphenylpyrazine (195). 

TABLE II.2 PYRAZINES PREPARED BY REDUCTION OF a-HYDROXYIMINO KETONES 

Substituted anilide analogues Substituted anilinocarbonyl analogues 234 

Evans and Mewett (233) prepared 2,5-di-r-butylpyrazine by zinc and alkali reduction of f-butylglyoxal dioxime but steric hindrance prevented formation of tetra-f-butylpyrazine when di-f-butylglyoxal monoxime was reduced with zinc and alkali. 

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Detailed discussion of the preparation of a variety of alkyl- and arylpyrazines by primary syntheses, principally from aliphatic components, appears in Chapter II. These include, for example, the preparation of 2,5-disubstituted and 2,3,5,6-tetrasubstituted alkyl- and arylpyrazines from a-amino carbonyl compounds, which may be produced by many methods such as reduction of a-hydroxyimino carbonyl compounds, aminolysis of a-halogeno carbonyl compounds, oxidation of a-amino... 

Preparations of C-acylpyrazines by primary syntheses have been described in Section II.IB by reduction of a-hydroxyimino carbonyl compounds (226-230). In addition to these preparations, reduction of 3-nitrosopentane-2,4-dione (prepared by nitrosation of pentane-2,4-dione) over Pd/C in an autoclave gave 2,5-diacetyl-3,6-dimethylpyrazine, and 2-nitroso-l-phenylbutane-l,3-dione (from 1 -phenylbutane-1,3-dione) similarly treated gave 2,5-dibenzoyl-3,6-dimethylpyrazine (1064). 

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