Carbon disulfide heterocyclics,

N-(2-thiazolyl)dithiocarbamates are prepared by the action of carbon disulfide on 2-aminothiazoles (see Section III.3.C and Ref. 505). When refluxed with secondary amines these heterocyclic dithiocarbamates yield l,T-dialkyl-3-(2-thiazoIyI)thioureas (261) (491). 

Treatment of the heterocycle, 38 (obtained from ethylene-diamine and carbon disulfide), with nitrous acid affords the N-nitroso compound, 39. Reduction with zinc leads to the corre-... 

Slow evaporation of a solution of 4 in carbon disulfide gives the orange ten-membered heterocycle 6.39 ... 

This silylene formation from 27 under mild conditions permits the synthesis of a variety of interesting carbo- and heterocycles, most of which are new types of compounds. The results are summarized in Schemes 5 and 6. The reactions with benzene and naphthalene represent the first examples of [2+1] cycloadditions of a silylene with aromatic C=C double bonds.59 623 The reactions with carbon disulfide and isocyanide (Scheme 6) are also of great interest because of their unusual reaction patterns.62b... 

In his approach toward selenium-containing heterocycles with potential biological activity, Abdel-Hafez reacted 2-amino-3-(4,5-dihydro-17/-imidazol-2-yl)-4,5,6,7-tetrahydro-l-benzoselenophene 297 with triethyl orthoformate and benzaldehyde to generate the tricyclic systems 296 and 298, respectively (Scheme 21) <2005RJ0396>. Similarly, reaction with carbon disulfide gave the corresponding thiourea 299. 

There is an enormous literature on thiocarbonyl compounds, due in part to the technical and industrial importance of many of them, including thioamides, thioureas, xanthates, dithiocarbamates and so forth. An excellent, and recent, general review is available.107 There are also specialized reviews germane to the present chapter Griffin, Woods, and Klayman2 discussed the use of thioureas in the synthesis of heterocycles the preparation of thiazoles from thioamides is included in a three-part volume on Thiazoles 108 the use of carbon disulfide in the synthesis of trithiones and related heterocycles has been reviewed by Mayer109 and Huisgen110 has reported numerous examples of 1,3-dipolar cycloadditions in which carbon disulfide was used. 

Phosphorus pentasulfide is used to replace oxygen atoms with sulfur atoms the reaction is commonly carried out in a solvent heated under reflux. Solvents employed include carbon disulfide, aromatic hydrocarbons, and pyridine. If an oxygen atom is part of a heterocycle, then the reagent may replace it with sulfur, as in the formation of 2,1-benzisothiazoles from 2,1-benzisoxazoles.119 Such replacements are, however, not general some prior ring opening appears to be necessary before the reagent can act. For example, under normal conditions furan is not attacked. 

Mesoionic 1,2,3,4-oxatriazolium-5-thiolates (172) are convenient starting materials for mesoionic thiatriazole 5-oxides. Thus arylhydrazines and carbon disulfide in ethanol yield arylhydrazinium dithiocarbamate salts, which are nitrosated with sodium nitrite in aqueous hydrochloric acid to give yellow l,2,3,4-oxatriazolium-5-thiolates (172). These heterocycles are isomerized by warming with ammonium hydroxide in ethanol to give colorless crystalline l,2,3,4-thiatriazolium-5-olates (173) (Scheme 36) <76CC306>. 

Thietes, four-membered precursors for the synthesis of 1,3-dilhianes or 1,3-oxathianes, provide access to the target heterocycles by reacting with either carbon disulfide and Lil <2002IJB1234, 2003S340> or, when the ring system denoted in Scheme 110 is aromatic, with diethyl 2-oxomalonate via a [4-1-2] cycloaddition pathway <1998JHC1505>. 

Robert and co-workers (239,240) discovered novel conversions of 2-amino-1,3-dithiolium-4-olates (348) into other mesoionic heterocycles. For example, reaction of 348 with carbon disulfide, phenyl isocyanate, or phenyl isothiocyanate affords l,3-dithiolium-4-thiolates (349), l,3-thiazolium-4-olates (350), and 1,3-thiazolium-4-thiolates (351), respectively. Some of these reactions proceed via the ring-opened ketene tautomer of 348 (240). 

These anhydro-bases are heterocyclic equivalents of enamines and enol ethers and react readily with electrophilic reagents to give products which can often lose a proton to give a new resonance-stabilized anhydro-base. Thus, anhydro-l,2-dimethylpyridinium hydroxide (645) reacts with phenyl isocyanate to give an adduct (646) which is converted to the stabilized product (647 - 648). A similar sequence with carbon disulfide yields the dithio acid (644). 

Other heterocyclic systems that do not belong to the structural types discussed in the preceding sections will now be considered. Silylenamines react with carbon disulfide to form a trithione derivative (119) (86CB257). Enaminoketones and carbon disulfide react in the same fashion (91JHC1245). 

The readily accessible enamines react with carbon disulfide and sulfur under mild conditions to produce l,2-dithiole-3-thiones (3b) via 3-amino dithioacids (Scheme 24), The nucleophilic character of the enamines is necessary for the initial reaction and to activate the sulfur (from Sg) for further insertion (67AG(E)294). Modified procedures produce other heterocycles. The yields of thiones (3b) may be low but this versatile reaction produces thiones that may be otherwise difficultly accessible, especially by direct sulfurization procedures, e.g. 1-morpholinocyclohexene may be converted into tetrahydrobenzo-1,2-dithiole-3-thione (142) in 40% yield. By contrast, direct sulfurization of 1-methylcyc-lohexene gives benzo-l,2-dithiole-3-thione (77b). Even dihydronaphtho-l,2-dithiole-3-thione (143) may be made by this procedure, although this compound may be dehydrogenated readily by sulfur at 220 °C. 

The synthesis of 4,5-dicyano-l,2,3-trithiole 2-oxide (172) starts from sodium cyanide and carbon disulfide which via (170) gave the disodium salt of 2,3-mercaptomaleonitrile (171 M = Na). Treatment of the corresponding silver salt (171 M = Ag) with thionyl chloride yielded (172) <66HC(2l-l)l). Phenylsulfine (174), prepared in situ by dehy-drohalogenation of phenylmethanesulfinyl chloride (173), slowly decomposed in ether solution at room temperature to give cis- and trans-stilbenes, mms-4,5-diphenyl-l,2,3-trithiolane 1,1-dioxide (36) and a 5,6-diphenyl-l,2,3,4-tetrathiane dioxide (68JCS(C)1612). The mechanisms of formation of these heterocycles are obscure. 

On the use of carbon disulfide for synthesizing sulfur-containing heterocyclic compounds see Mayer and Gewald.62 Compounds of type 8 prepared by the procedure described above are listed in Table VI. 

Bis(trifluoromethyl)diazomethane is a reactive, electrophilic compound. It forms adducts with nucleophiles such as amines and phosphines5 and adds to olefins, acetylenes,5 and thiocar-bonyl compounds6 to form heterocycles. It has been used as a source of bis(trifluoromethyl) carbene in reactions with benzene,5 saturated hydrocarbons,7 carbon disulfide,8 and transition metal compounds,8 and it undergoes a unique radical chain reaction with saturated hydrocarbons to form adducts that are hydrazoncs and azines.7... 

Addition of anionic nucleophiles to alkenes and to heteronuclear double bond systems (C=0, C=S) also lies within the scope of this Section. Chloride and cyanide ions are effieient initiators of the polymerization and copolymerization of acrylonitrile in dipolar non-HBD solvents, as reported by Parker [6], Even some 1,3-dipolar cycloaddition reactions leading to heterocyclic compounds are often better carried out in dipolar non-HBD solvents in order to increase rates and yields [311], The rate of alkaline hydrolysis of ethyl and 4-nitrophenyl acetate in dimethyl sulfoxide/water mixtures increases with increasing dimethyl sulfoxide concentration due to the increased activity of the hydroxide ion. This is presumably caused by its reduced solvation in the dipolar non-HBD solvent [312, 313]. Dimethyl sulfoxide greatly accelerates the formation of oximes from carbonyl compounds and hydroxylamine, as shown for substituted 9-oxofluorenes [314]. Nucleophilic attack on carbon disulfide by cyanide ion is possible only in A,A-dimethylformamide [315]. The fluoride ion, dissolved as tetraalkylammo-nium fluoride in dipolar difluoromethane, even reacts with carbon dioxide to yield the fluorocarbonate ion, F-C02 [840]. 

Heterocyclic spirans are prepared by [Ni(CO)4]-promoted tandem cycloaddition of diphenylcyclopio-panone (100) to isothiocyanates (101 equation 43) or to carbon disulfide (105 equation 44). When an equimolar mixture of (100), (101) and [Ni(CO)4] is allowed to react in DMF at 65-70 C, two heterocyclic spirans, pyrrolin-2-one-5-spiro-5 -thiolen-4 -one (102), and (103), are formed in addition to the pyrroline derivative (104). Similarly, carbon disulfide (105), reacts with (100) to give thiolen-2-one-5-spiro-5 -thiolen-4 -one (106) along with a small amount of 1 1 cycloadduct (107). ... 

The reagents used for the completion of the purine heterocycle are essentially the same as those used for the Traubc synthesis. The purine ring is formed by condensation with derivatives of formic acid or other carboxylic acids. Alternatively, formylation of the amino group is accomplished by a mixture of formic acid and acetic anhydride followed by cyclization. Alkyl esters or trialkyl ortho esters are also versatile synthons for ring closure. Moreover, heating in formamide or cyclization with urea or thiourea provides a satisfactory route. Condensations with isothiocyanates show unusual versatility leading to 2-sulfanylpurin-6-ols. From carbonic acid derivatives, cyclization is reported with chlorocarbonic esters, diethyl carbonate or carbon disulfide. 

Thiourea (98) was first prepared in 1870 by heating ammonium thiocyanate (99) (Scheme 54). The reaction is analogous to the historic preparation of urea (Wohler, 1828) which involved heating ammonium cyanate. Thioureas generally are stable crystalline solids which are useful in the synthesis of heterocyclic compounds. Symmetrical thioureas (100) may be obtained by the action of amines on carbon disulfide, and the procedure can be extended to the synthesis of cyclic thioureas (101) (Scheme 55). The reaction occurs via the intermediate (102) which on subsequent treatment with either ammonia or an amine yields the corresponding... 

---