3.5- Dichloro-1 -methyl-2 pyrazinone

I -Benzyl-3,6-dichloro-2( l//)-pyrazinonc (127, R = Cl) gave l-benzyl-5-chloro-3-methyl-2(17/)-pyrazinone (127, R = Me) [Me4Sn, Pd(PPh3)4, PhMe, reflux, <5 days residue from evaporation, KF, AcOEt, 20°C, 12 h 81%) or its 3-ethyl ho-mologues (127, R = Et) (Et4Sn, likewise 95%) 391 analogues similarly.391... 

Mcthyl-5-phenyl-2(l//)-pyrazinone (4) gave 2-chloro-3-methyl-5-phenylpyra-zine (5) (P0C13,175°C, sealed, 18 h 92% beware of pressure within the tube even when cooled ) 57 such a sealed reaction also converted 5-chloro-3-phcnyl-2( l//)-pyrazinone into 2,5-dichloro-3-phenylpyrazine (6) (185°C, 5 h 92%).1382... 

Dichloro-l-methyl-2(l//)-pyrazinone (142) gave 5-chloro-3-isothiouronio-l-mcthyl-2(l//)-pyrazinonc hydrochloride (143) [H2NC(=S)NH2, EtOH, 20°C, 3 h 71%], and thence 5-chloro-l-methyl-3-thioxo-3,4-dihydro-2(17/)-pyrazinone (144) (2.5 M NaOH, reflux, 1 h 75%) analogues likewise. ... 

Dichloro-l-methyl-2(177)-pyrazinone (188, R = Cl) gave selectively 6-chloro-4-methyl-3-oxo-3,4-dihydro-2-pyrazinecarbonitrile (188, R = CN) [CuCN, l-methyl-2-pyrrolidmone (solvent), 150°C, 6h 68%] ... 

The behavior of halogeno substituents on 1-substituted 2(lT/)-pyrazinones is similar to that in the fully aromatic systems. Thus, 1-methyl- and 1-phenyl-3,5-dichloro-2(17/)-pyrazinones undergo nucleophilic substitution at C-3 with hydrazine and thiourea, whereas in a 5-chloro compound displacement is suppressed <86JHC113>. 

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