Pyrazinethiones

This synthesis is also represented by only one example. 3-Ethoxycarbony-lamino-l//-pyrazino[2,3-e][l,3,4]thiadiazine (125) in methanolic hydrogen chloride under reflux during 2 h furnished 3-(4-ethoxycarbonylsemicarbazido)-2(l//)-pyrazinethione (126) in 32% yield.284... 

The conversion of halogenopyrazines into pyrazinethiones is usually done either with sodium hydrogen sulfide solution or by initial treatment with thiourea and subsequent hydrolysis of the intermediate isothiouronium salt (frequently unisolated). A third method, involving treatment of the halogeno substrate with thiosulfate, has proven promising in some heterocyclic series but not so far in the pyrazines 2-chloropyrazine did so give 2(1 //)-pyrazinethionc but only in 20% yield.1358... 

This section is mainly about tautomeric pyrazinethiones but the meagre available information on nontautomeric pyrazinethiones and pyrazinethiols is also included. 

Aspects of the tautomerism of tautomeric pyrazinethiones have been studied931, 1398,1424 all(j le acute toxicities of 2-mercaptomethylpyrazine and bis(pyrazin-2-yl-methyl) disulfide have been determined.674 1204... 

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 ... 

Diisopropyl-2(l//)-pyrazinethione gave 2-ethoxycarbonylmethylthio-3,6-diisopropylpyrazine (25) (Et02CCH2Cl, Na2C03, AcMe, 20°C, 15 h ... 

Note There appear to be no regular aminolyses in recent literature but the example here amounts to a de facto aminolysis of a nontautomeric pyrazinethione. 

All the important routes to alkylthiopyrazines have been discussed already by primary synthesis (Chapters 1 and 2), by alkanethiolysis of halogenopyrazines (Sections 4.2.5 and 4.4), or by S-alkylation of pyrazinethiones (Section 6.1.2). The remaining minor routes are either unrepresented in recent literature or are illustrated in the following examples ... 

The dealkylation of alkylthiopyrazines to pyrazinethiones has been covered already (Section 6.1.1). Of the other possible reactions of alkylthiopyrazines, those represented in recent literature are discussed in the following subsections. 

The formation of such pyrazines by primary synthesis has been covered in Chapters 1 and 2 the meagre literature on their formation by oxidation of pyrazinethiones or pyrazinethiols is mentioned in Section 6.1.2. 

By aminolysis of tautomeric pyrazinethiones (nuclear primary, secondary, tertiary) Section 6.1.2. 

Acetamido-2(l//)-pyrazinethione 3-Acetanudo-20 //)-pyrazinone 2-Acetonyl-5,6-diphenylpyrazine 2-Acetonyl-6-methylpyrazine 2-Acetonyl-3-phenylpyrazine 2-Acetonyl-6-phenylpyrazine 2-Acetonylpyrazine... 

Amino-5,6-diphenyl-2-pyrazinecarbothioamide 3-Amino-5,6-diphenyl-2-pyrazinecarboxamide 3-Amino-5,6-diphenyl-2-pyrazinecarboxylic acid 3-Amino-5,6-diphenyl-2(177)-pyrazinethione 1 - Amino- 3,5 - dipheny lpy razinium (+ anion)... 

Amino-6-methyl-2(l//)-pyrazinethione l-Amino-3-methylpyrazinium iodide 3-Amino-l-methyl-2(l//)-pyrazinone 3-Amino-5-methyl-2(l//)-pyrazinone 3-Amino-6-methyl-2(l//)-pyrazinone... 

Methoxy- 2(1 77)-pyrazinethione 3 -Methoxy- 2(1 77)-pyrazinone 6-Methoxy-2(177)-pyrazinone 2-Methoxy-3-trimethylsilylpyrazine Methyl 6-acetamido-2-pyrazinecarboxylate Methyl 3-acetoxy-2-pyrazinecarboxylate Methyl 5-acetoxy-2-pyrazinecarboxylate Methyl 6-acetoxy-2-pyrazinecarboxylate Methyl 5-acetyl-3-amino-2-pyrazinecarboxylate Methyl 6-acetyl-3,5-diamino-2-pyrazinecarboxylate Methyl 5-allylamino-3-amino-6-chloro-2-pyrazinecarboxylate... 

Methyl-5,6-diphenylpyrazine 4-oxide l-Methyl-5,6-diphenyl-2(l//)-pyrazinethione... 

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