Pyridine-2-thione, 3-amino cyclization

Cycloaddition and cyclization routes were used to access certain 1,3-diazines. The 4+2 cycloaddition reaction of 4-(N-allyl-N-aryl)amino-l,3-diaza-l,3-butadienes with vinyl-, isopropenyl-, and chloroketene led to pyrimidinone-fused pyrimidinones <97T13841>. Cis-cyclopenta[d]pyrimidines were derived from cis-2-amino-l-cyclopentanecarboxylates by cyclization with KOCN and KSCN <97JHC1211>. 2-Thioxopyrido[3, 2 4,5]thieno[3,2-r/]pyrimidin-4(3//)-ones 19 were prepared by cyclocondensation of 2-carbethoxy-3-amino-4-phenyl-6-substituted-thieno[2,3-/)]pyridines and isothiocyanates <97JHC937>. Thiazolyl-benzimidazoles derived from 2-cyanomethyl-l//-benzimidazole and 2,3-dihydrothiazole-2-(3//)-thiones were cyclized to the corresponding thiazolo[4,5-r/]pyrimidines <97PHA346>. Reductive cyclization of 6-cyanomethyl-5-nitropyrimidines afforded 7-alkyl-5//-pyrrolo[3,2-r/]pyrimidines and 6-amino-7,7-dialkyl-7//-pyrrolo[3,2-rf]pyrimidines <97T391>. 7-Methyl-5-alkyl-2-vinyl-pyrazolo[3,4-r/]pyrimidine-4,6(5//,7//)-diones arose from cyclization and alkylation of... 

Reaction of 4-arylidene-2-phenyl-5(4//)-oxazolones 593 with A-phenacylpyri-dinium bromide proceeds by the same sequence to give oxazolo[5,4-/>]pyridines 594 (Scheme 7.188) while the reaction of 4-(aminomethylene)-2-phenyl-5(4//)-oxazolone 418 and phenyl isothiocyanate gives pyrimidin-2-thiones 595 (Scheme 7.189). In this latter case initial attack of the exocylic amino group produces an intermediate thiourea (not shown) that subsequently cyclizes to 595. 

A Thorpe-Ziegler intramolecular cyclization starting with 3-cyanopyridine-2-thione derivatives leads to the formation of 3-amino-2-(organylsulfinyl)thieno[2,3- ]pyridines in high yields <2006RCB529>. 

Heating equimolar amounts of 5-amino-l-methyIimidazoIe-2(3i/)-thione (391) with diethyl ethoxymethylenemalonate (390) gave the diethyl ester of [(5-amino-2,3-dihydro-l-methyI-2-thioxo-lH-imidazoI-4-yI)methyIene]propanedioic acid (392), which cyclized in 10% aqueous sodium hydroxide to 6-ethoxycarbonyI-3-methyI-2(lH)-thioxoimidazo[4,5-h]pyridin-5(4H)-one (393) (78H(lO)24i). 

A derivative of a hitherto unknown nucleus was produced when 4-amino-5-aminomethyl-3-methyltriazole was refluxed with carbon disulfide and triethylamine in pyridine, which yielded 3-methyl-3,7-dihydro-l,2,3-triazolo-[4,5-d][l,3]thiazine-5-thione (98) (3 hr, 53%) the 3-benzyl analog was made similarly (63%) [80JCS(P1)2009]. Cyclization of 4-anilino-5-ethoxycarbonyltriazole with polyphosphoric acid produced 1 f/-triazolo-[4,5-h]quinol-4-one (99) [80EUP(A)2562]. Similarly, ring closure of 4-(2-pyridylamino)triazole-5-carboxylic acid (or its esters) gave l//-pyrido-[l,2-a]-l,2,3-triazolo[4,5-d]pyrimidin-4-one (100) (77GEP2757929). 4-Amino-5-formyl-3-methyltriazole and pentane-2,4-dione, set aside in 20% sulfuric acid, yielded 3,5-dimethyl-3//-l,2,3-triazolo [4,5-6] pyridin-6-yl... 

These isomers (XLVIII) are formed as side-products during the cycUzation reaction or when the 2,3-dihydro-l,2,4-triazolo[4,3-a]pyri-midine-3-thiones (XLVII) are heated either in water or water-pyridine mixtures. These isomerisations are probably proceeded by the hydrolysis of the (XLVII) first formed. The hydrolysis likely yields either the Schiff s base of 5-amino-2l4-l,2,4-triazoline-3-thione (XLIXa) or 5-amino-zl4-l,2,4-triazoline-3-thione (XLIXb) and the corresponding -dicarbonyl compound. These substances can now cyclize again either on the Nj or the nitrogen atom. This re-cyclization however will occur most readily on the more nucleophile nitrogen atom of the hydrazino function (Nj). Similar conversion reactions are known and have been studied in detail for the non-thioxo substituted l,2,4-triazolo[4,3-a] pyrimidines 3, 317, 318, 319, 383). 

A variety of methods has been described for the synthesis of l,3-dithiole-2-thiones (233), well-known precursors for the generation of 1,3-dithiole derivatives. / -KetoW,)V-dialkyldithio-carbamates (234) are easily cyclized with cone, sulfuric acid or 70% perchloric acid to yield the corresponding 2-amino-1,3-dithiolylium salts (235), which upon treatment with hydrogen sulfide in methanol or pyridine, afford the l,3-dithiole-2-thiones (233) in excellent yields (Scheme 47) <64JOC1703, 67ZC58, 77TL2579>. 

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