2-Hydroxypyrazine 5.6- disubstituted

Direct ring syntheses are also available for the preparation of hydroxypyrazines. Thus, haloacylation of an a-aminoketone, followed by reaction with ammonia and oxidation represents a general synthesis of 5,6-disubstituted and 3,5,6-trisubstituted 2-hydroxypyrazines.339 This is illustrated by the preparation of 5,6-dimethyl-2-hydroxy-pyrazine (Scheme 39). Hydroxypyrazines are very conveniently... 

A variation of this procedure was introduced by Tota and Elderfield (248), who described a general synthesis for 2,3-disubstituted and 2,3,6-trisubstituted 5-hydroxypyrazines. In this reaction an a-(bromoacetylainino) carbonyl compound (17) [prepared from an a-amino carbonyl compound (15) with a bromoacetyl bromide (16)] was treated with alcoholic ammonia to give the corresponding pyrazine (18). The reaction is discussed in more detail in Section 7. 

Tota and Elderfield (248) have described a general synthesis for 2,3-disubstituted and 2,3,6-trisubstituted 5-hydroxypyrazines. In this reaction an a-(bromoacetyl-amino) carbonyl compound (prepared from an a-amino carbonyl compound with... 

In an attempt to force the condensation of an a-aminohydroxamic acid and a potential a-keto aldehyde to give 3,6-disubstituted 2-hydroxypyrazine 1-oxides, Dunn and co-workers (545, 546) studied the condensation of a-aminohydroxamic... 

The preparation of 3,6-disubstituted 2-hydroxypyrazine 1-oxides from (11), which were derived from a-aminohydroxamic acids and a,fl-unsaturated a-bromo-... 

Bromination of 5-s-butyl-3-hydroxy-2-isobutylpyrazine (deoxyaspergillic acid) in aqueous solution or acetic acid gave 2-bromo-3-s-butyl-5-hydroxy-6-isobutylpyrazine (bromodeoxyaspergjllic acid) (87) bromination of 2-s-buty-3-hydroxy-5-isobutyl-pyrazine in acetic acid gave 2-bromo-6-s-butyl-5-hydroxy-3-isobutylpyrazine (93) and 3-hydroxy-2,5-diphenylpyrazine behaved similarly (282). This procedure with bromine in acetic acid was unsatisfactory when applied to simpler hydroxypyrazines (817), and bromination of 3,6(and 5,6)-disubstituted-2-hydroxypyrazines and 2-... 

---