Thiation

Numereous derivatives of benzimidazole, naphthoimidazoles and other condensed imidazole systems can be very effectively thiated with elemental sulfur on heating without solvent at 230-260°C. The product of this reaction is the corresponding imidazolin-2-thione formed in excellent yield (67ZOR1518, 95IZV2231). For example, imidazo[4,5-cjpyridines (329, R =H, Aik, Ar, C6H5CH2) gave 1,3-dihydro-2//-imidazo[4,5-c]pyridine-2-thiones (330). 

By analogy, imidazolium salts, e.g. (331), can be converted with a high yield into the corresponding 2-thione or 2-selenone derivatives (332) by heating with sulfur or selenum in DMF in the presence of triethylamine (90CHE1689). 

Thiation of N-substituted 1,2,4-triazole has been also achieved (93ZOR1896). 

The mechanism of the thiation reaction is unknown, though in the case of quaternary salts one can suppose that it includes formation of the corresponding carbene as a possible intermediate. 

3- one 234 with arylsulfenyl chlorides 235a-c that gave the corresponding 

4- arylthiopyrazoles 236a-c as major tautomers and 4-arylthiopyrazol-3-ones 237a-c as minor tautomers. The reaction with phenylsulfenyl chloride required 

These condensations involve position 4 of pyrazol-3-ones and aldehydes, ketones, a,/J-unsaturated carbonyl compounds, doubly activated methylene compounds containing carbonyl functionalities or nitroso compounds. 

Since 1964 a large number of reports describe the condensation of 2,4-dihydro-pyrazol-3-ones with aryl aldehydes. In contrast condensation of 1,2-dihydropyrazol- 

3- ones with aryl aldehydes have been reported on only three occasions. Most 

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Pyrimidine-4/6-thiones (and occasionally 2-thiones) can be made by thiation of the corresponding pyrimidinones providing that there are no sensitive groups present. The method is summarized and exemplified in Section 2.13.2.2.7/). 

O-Alkylation of the readily available iV-unsubstituted azetidin-2-ones (/3-lactams) constitutes a versatile route to 2-alkoxy-l-azetines (cf. Section 5.09.3.2.3). Thus treatment of the /3-lactams (266) with trialkyloxonium tetrafluoroborates followed by basification affords the 2-alkoxy-l-azetines (267) in moderate yields (67JHC619,69LA(725)124). Similar treatment of the azetidine-2-thiones (268) (available from thiation of the corresponding /3-lactams with phosphorus pentasulfide) affords the analogous 2-ethylthio-1-azetines (269) (67JHC619), which are generally more stable than their 2-alkoxy analogues. 

Hypoxanthine, 2-trifluoromethyl-synthesis, 5, 587 Hypoxanthine, trimethylsilyl-glycosylation, 5, 536 Hypoxanthinium nitrate, 1,3,7-trimethyl-thiation, 5, 540 Hypsochromic shift, 1, 344... 

Purine, 6,8-dioxo-1,6,7,8-tetrahydro-methylation, 5, 534 synthesis, 5, 596 thiation, 5, 557... 

Purine, 6,8-dioxo-2-thioxo-l,2,3,6,7,8-hexahydro-thiation, 5, 557 Purine, 2,6-dithioxo-synthesis, 5, 574, 590 Purine, 2,8-dithioxo-synthesis, 5, 578... 

Purines, N-alkyl-N-phenyl-synthesis, 5, 576 Purines, alkylthio-hydrolysis, 5, 560 Mannich reaction, 5, 536 Michael addition reactions, 5, 536 Purines, S-alkylthio-hydrolysis, 5, 560 Purines, amino-alkylation, 5, 530, 551 IR spectra, 5, 518 reactions, 5, 551-553 with diazonium ions, 5, 538 reduction, 5, 541 UV spectra, 5, 517 Purines, N-amino-synthesis, 5, 595 Purines, aminohydroxy-hydrogenation, 5, 555 reactions, 5, 555 Purines, aminooxo-reactions, 5, 557 thiation, 5, 557 Purines, bromo-synthesis, 5, 557 Purines, chloro-synthesis, 5, 573 Purines, cyano-reactions, 5, 550 Purines, dialkoxy-rearrangement, 5, 558 Purines, diazoreactions, 5, 96 Purines, dioxo-alkylation, 5, 532 Purines, N-glycosyl-, 5, 536 Purines, halo-N-alkylation, 5, 529 hydrogenolysis, 5, 562 reactions, 5, 561-562, 564 with alkoxides, 5, 563 synthesis, 5, 556 Purines, hydrazino-reactions, 5, 553 Purines, hydroxyamino-reactions, 5, 556 Purines, 8-lithiotrimethylsilyl-nucleosides alkylation, 5, 537 Purines, N-methyl-magnetic circular dichroism, 5, 523 Purines, methylthio-bromination, 5, 559 Purines, nitro-reactions, 5, 550, 551 Purines, oxo-alkylation, 5, 532 amination, 5, 557 dipole moments, 5, 522 H NMR, 5, 512 pJfa, 5, 524 reactions, 5, 556-557 with diazonium ions, 5, 538 reduction, 5, 541 thiation, 5, 557 Purines, oxohydro-IR spectra, 5, 518 Purines, selenoxo-synthesis, 5, 597 Purines, thio-acylation, 5, 559 alkylation, 5, 559 Purines, thioxo-acetylation, 5, 559... 

Pyrimidin-2( 1H) -one, 4-benzyl-5-phenyl-3,4-dihydro-synthesis, 3, 118 Pyrimidin-2(1 H)-one, 5-bromo-thiation, 3, 89... 

Quinazolin-4(3H)-one, 3-phenyl-reduction, 3, 75 Quinazolinones polymers, 1, 298 reactions, 3, 89 structure, 3, 66-67 synthesis, 2, 96 3, 133 thiation, 3, 89 Quinazolin-4-oties 2,3-disubstituted Grimmel synthesis, 3, 109 mass spectra, 2, 22... 

THIATION WITH 2.4-BIS(4-NETHOXYPHENYL)-1.3.2.4-DITHIADIPHOSPHETANE 2.4-01SULFIDE N-ICTHYLTHlOPYRROLIDONE... 

The thiation procedure described here is an example of a general synthetic method for the conversion of carbonyl to thiocarbonyl groups. Similar transformations have been carried out with ketones, carboxamides,esters,thioesters, 1 actones, " thiol actones, - imides, enaminones, and protected peptides. ... 

The course of thiation (replacement of oxygen by sulfur) of dioxo-... 

Thiation was most frequently carried out in pyridine - for unsubstituted compounds which are considerably polar, this is a prerequisite. The less polar iV-alkylated derivatives can be thiated in toluene or xylene for thiation of 6-azathymine, tetralin was also used. ... 

The cyclization of some 2- and 4-methylthiosemicarbazones and the thiation of the cyclic product was recently studied by Zee-Cheng and Cheng. ... 

This conversion may be done indirectly via halogenoquinoxalines (Sections 3.1.1 and 3.2.3), but direct thiation with phosphorus pentasulfide/pyridine or with Lawesson s reagent (43) is less time-consuming. The following examples illustrate typical direct procedures. 

Most tautomeric quinoxalinethiones hae been made by primary synthesis (see Chapter 1), by thiolysis of halogenoquinoxalines (see Section 3.2.3), or by thiation of quinoxalinones (see Section 4.1.2.1) most nontautomeric quinoxalinethiones by primary synthesis (see Chapter 1) or by thiation of the corresponding quinoxalinones (see Section 4.5.2) and an occasional extranuclear quinoxalinethiol by... 

Styryl-2(l//)-quinoxalinone (29) underwent a one-pot thiation and cyclization to give 2-phenylthieno[2,3-/7]quinoxaline (30) (P2S5, pyridine, reflux, 10 h 55%). ... 

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