3-Phenyl-2 -pyrazinone 4-oxide

Condensation of phenylalaninenitrile, prepared from phenyl acetaldehyde, with 1-oxime of pyruvaldehyde afforded the pyrazine N-oxide, which was further rearranged to give the N-acetyl pyrazinone. The acetyl groups were removed by treatment with hydrazine to give the target 6-aminopyrazinone. 

Heating with phosphoryl chloride converted 1 -hydroxy-3-phenyl-2( 1H )-pyrazinone (52) into the 2,5-dichloro derivative (53) via the 5-monochIoro species. It had been expected that chlorination would take place at C-6, but this occurred only to a minor extent. The observed chloride attack /3 to the oxygen function might be accounted for in terms of the sequence illustrated in Scheme 46 (86JHC149). Reaction mechanisms have been proposed to explain the observed a- and /3-chlorination when 2- and 3-substituted pyrazine Af-oxides are subjected to the Meisenheimer reaction. /3-Chlorination was rationalized in terms of electron withdrawal by the unoxidized nitrogen atom [84JCR(S)318] (Scheme 46). 

Chloro-3-isobutylpyrazine 4-oxide gave 3-isobutyl-2( I // )-pyrazinone 4-oxide (111, R = Hu ) (5 M NaOH, reflux, 2 h 39%) 86 2-chloro-3-phenylpyrazine 4-oxide gave 3-phenyl-2( I //(-pyrazinone 4-oxide (111, R = Ph) (KOH, H20—EtOH, reflux, 1 h 30%) 1290 also analogues likewise.1290... 

Amino-6-phenyl-2-pyrazinecarboxamide from its 4-oxide (257) (Na2S204, H20, reflux, 24 h 97%) 1517 also substituted-phenyl analogues likewise.1517 6-Phenyl-2( I //(-pyrazinone from its 4-oxide (258) (Na2S204, EtOH—H20, reflux, 30 min then more Na2S204, reflux, 30 min 59%).88 Also other examples.1457... 

Bromo-5-phenyl-2(l//)-pyrazinone 5-Bromo-3-phenyl-2(l//)-pyrazinone 5-Bromo-3-piperidino-2-pyrazinamine 2-Bromo-5-piperidinopyrazine 4-oxide... 

Ethyl-3-methyl-5-phenyl-2(177)-pyrazinone 5-Ethyl-3-methyl-2-pyrazinamine 1-oxide 2-Ethyl-3-methylpyrazine... 

Hydroxy-6-methyl-3-phenyl-2(17/)-pyrazinone from its 4-oxide (259) (T1CI3,... 

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