Extranuclear Hydroxypyrazines

Many such hydroxypyrazines have been made by primary synthesis (see Chapters 1 and 2), some by C- or N-hydroxyalkylation procedures (see Sections 3.1.1.1 and 3.2.2.1), and a few by hydrolysis of extranuclear halogenopyrazines (see Section 4.4). Other preparative routes are illustrated in the following classified examples ... 

Extranuclear hydroxypyrazines react as alcohols or phenols according to the type of substituent that bears the hydroxy group. Already covered are their conversion into alkenylpyrazines by dehydration (Section 3.2.1.5) or into extranuclear halogenopyrazines (Section 4.3.1). 

The reduction of pyrazinecarboxylic acids to extranuclear hydroxypyrazines has been covered in Section 5.2.1. Other reactions are illustrated by the following classified examples ... 

PREPARATION OF HYDROXYPYRAZINE A-OXIDES AND EXTRANUCLEAR HYDROXYPYRAZINE A-OXIDES... 

Oxidation of nuclear and extranuclear hydroxypyrazines (and derivatives) to their Af-oxides has been achieved with hydrogen peroxide in acetic acid, and with m-chloroperoxybenzoic acid in 1,2-dichIoroethane. 3-Hydroxy-2,5-diisobutyl-pyrazine was oxidized with 30% hydrogen peroxide in acetic acid at 70 to 3-hydroxy-2,5-diisobutylpyrazine 1-oxide (101), 3-hydroxy-2-(Af-methyl-A -phenyl-carbamoyl)pyrazine 1-oxide (90) was also prepared from the conesponding pyrazine [its A -4-methyl derivative was prepared similarly and also by methylation of (90) (1055)], and 3-hydroxy-2-(A -methyl-AAp-tolylcarbamoyl)pyrazine 1-oxide (1055) was synthesized analogously. 

Several reactions of pyrazinecarboxylic esters have been discussed already reduction to N-alkylpiperazines (Section 3.2.2.2), reduction to extranuclear hydroxypyrazines (Section 5.2.1), and hydrolysis to pyrazinecarboxylic acids (Section 8.1.1). Other reactions to be expected of carboxylic or carboximidic esters are typi-hed in the following class lied examples ... 

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