Preparation of Pyrazinethiones and Pyrazinethiols

Most tautomeric pyrazinethiones have been made by primary synthesis (see Chapters 1 and 2), thiolysis of halogenopyrazines (see Section 4.2.4), or thiation of tautomeric pyrazinones (see Section 5.1.2.1) a few nontautomeric pyrazinethiones by primary synthesis (see Chapters 1 and 2) or thiation of nontautomeric pyrazinones (see Section 5.4.2) and nearly all extranuclear pyrazinethiols by thiolysis of extranuclear halogenopyrazines (see Section 4.4). Other routes to such pyrazinethiones and pyrazinethiols are illustrated in the following examples  

5-Benzylthio-2(lZ/)-pyrazinone (1) gave 5-lhi()xo-3,4,5,6-tetrahydro-2(IZ/)-pyrazinone (3) (Na, liquid NH3, -76°C, 1 h 70%) a small yield of the intermediate 5-mercapto-2(l//)-pyrazinone (2) was obtained when the proportion of sodium to substrate was decreased ss 

5-Bismethylthio-3,6-dihydropyrazine (4) gave 3,6-dihydro-2,5(l//,4//)-pyra-zinedithione (6) by addition of H2S and subsequent loss of MeSH from the intermediate (5) (H2S J, pyridine-THF, 0°C, 3 h 64%)  

2-Methoxy-3-(p-methoxybenzylthio)pyrazine (8, R =OMe) gave 3-methoxy-2(l//)-pyrazinethione (9) [Hg(OAc)2, trace anisole, F3CCO2H, 0°C, 15 min residue from evaporation, NaBH4, H2O, 20°C, 90 min 87% also other examples)  

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