Reactions with sulfur heterocycles

A[ -Aiylthiocarbamoyl-N,N-dialkylamidines 150 are useful intermediates for many heterocyclic systems (1996T8413), one being a reaction with sulfur monochloride that led to dithiazoles 151 (Scheme 79). 

The various heterocyclic ligands just described are easily cleaved from the respective molybdenum centers either by reaction with sulfur or through ligand exchange with l,2-bis(diphenylphosphino)ethane (Scheme 17).44a The Diels-Alder cycloaddition is successfully expanded to transient 1-phospha-1,3-diene complexes such as 25 and suitable dienophiles. As illustrated in Scheme 12, the isomeric 1,2-dihydrophosphetes (e.g., 26) are their masked stable precursors. Reaction of 26 with dimethyl acetylenedicarboxy-late or with benzaldehyde furnishes the Diels-Alder adducts of transient 25, compound 71, as a mixture of two isomers, and isomerically pure 72.44b (See Scheme 18.)... 

The halogen atoms of the geminal dihalo derivatives of diaryl diketones and of heterocyclic ketones can be replaced in reactions with sulfur compounds 0e.g., sodium hydrogen sulfide, thioacetic acid, phosphorus pentasulfide), thioketones being formed.318,319 Staudinger and Freudenberger,320 for instance, obtained thiobenzophenone in 46% yield from benzophenone dichloride (dichlorophenylmethane) and a hot alcoholic solution of sodium hydrogen sulfide ... 

Ylides derived from imidazolium- and triazolium-substituted indole anions belong to the class of conjugated mesomeric betaines. Their tautomers are N-heterocyclic carbenes, which undergo trapping reactions with sulfur, selenium, and triethylborane, respectively. Deprotonation of the salts 45a—c with NaOH/EtOH produces the ylides 46a—c which are in tautomeric equihbrium with carbenes 47a—c (Scheme 36) (2014T8672). 

Subsequently, a formal [4+l]/[3+2] cycloaddition cascade reaction with sulfur ylides and nitroolefin derivatives 263 was carried out in a similar manner by the same group. The isoxazoline A-oxide 259 intermediates underwent a series of intramolecular reactions, affording fused heterocyclic structures 264 with excellent diastereoselectivities (Scheme 2.68) [97]. 

In the synthesis of commercial sulfur-heterocycles two interesting reactions are used (i) diphenylamines may be connected by a sulfur bridge in the orfho-positions (ii) the amino grouping of sulfonamides undergoes condensation reactions with neighboring imino- and amide groups. 

Vinyl chloride reacts with sulfides, thiols, alcohols, and oximes in basic media. Reaction with hydrated sodium sulfide [1313-82-2] in a mixture of dimethyl sulfoxide [67-68-5] (DMSO) and potassium hydroxide [1310-58-3], KOH, yields divinyl sulfide [627-51-0] and sulfur-containing heterocycles (27). Various vinyl sulfides can be obtained by reacting vinyl chloride with thiols in the presence of base (28). Vinyl ethers are produced in similar fashion, from the reaction of vinyl chloride with alcohols in the presence of a strong base (29,30). A variety of pyrroles and indoles have also been prepared by reacting vinyl chloride with different ketoximes or oximes in a mixture of DMSO and KOH (31). 

The latter reagent also methylates certain heterocyclic compounds (e.g., quinoline) and certain fused aromatic compounds (e.g., anthracene, phenanthrene). The reactions with the sulfur carbanions are especially useful, since none of these substrates can be methylated by the Friedel-Crafts procedure (11-12). It has been reported that aromatic nitro compounds can also be alkylated, not only with methyl but with other alkyl and substituted alkyl groups as well, in ortho and para positions, by treatment with an alkyllithium compound (or, with lower yields, a Grignard reagent), followed by an oxidizing agent such as Bra or DDQ (P- 1511). 

Thiadiazoles have proven of some utility as aromatic nuclei for medicinal agents. For example, the previous volume detailed the preparation of a series of "azolamide" diuretic agents based on this class of heterocycle. It is thus of note that the 1,2,5-thiadiazole ring provides the nucleus for a clinically useful agent for treatment of hypertension which operates by an entirely different mechanism, p-adrenergic blockade. In its preparation, reaction of the amide-nitrile 211 with sulfur monochloride leads directly to the substituted thiadiazole 212. ... 

Some enzymes have been found to be capable of conversion of the polyaromatic sulfur heterocycles in mixtures of an aqueous phase containing buffer+water-miscible solvent and a water-immiscible solvent. For example, conversion of thiophenes and sulfides was demonstrated in an aqueous system with 20% acetonitrile in contact with 0.2% diesel. A process for sulfur removal was designed based on this reaction [394], Additional details were given in Section 4.2.1. In a subsequent study effect of this system on PAH... 

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. 

A number of benzo- or dibenzo-fused seven membered phosphorus heterocyclic systems have also been studied. These include the benzo-fused oxa-bridged phosphaalkene 76 prepared by thermolysis of 2,3-diphenylindenone 23-epoxide (as a source of the carbonyl ylide 1,3-dipole intermediate) in the presence of /-butylphosphaalkyne. This bridged phosphaalkene is unusually stable even without inert gas blanketing . Reaction of 76 with sulfur or grey selenium stereoselectively affords the thia- or selenaphosphiranes 77 (X = S, Se respectively). <00T6259>... 

A similar reaction takes place with sulfuric acid. It takes 2 to 3 months to achieve thermodynamic equilibrium between 5- and 6-membered heterocycles. However, the ratio of the products may be easily predicted in several minutes measuring the ratio of intensities of peaks of [M — CH3]+ and [M — C2H4]+ ions in an El mass spectrum of the initial substituted arylcyclopropane [23]. 

No new calculations were specifically devoted to this heterocylic system since CHEC-II(1996). Redox properties of chalcogeno-ureas possessing this heterocyclic skeleton and resulting from the reaction of Arduengo carbenes such as 108 with sulfur or selenium was investigated through semi-empirical calculations <2000EJI1935>. 

Few examples have been reported of metals coordinated to six-membered boron-sulfur heterocycles. Ashe et al. prepared 4-methyl-l,4-thiaborin (SC4H4BMe) which forms a stable molybdenum tricarbonyl sandwich complex 144.158 jn g etjert s laboratory, the reaction of the diborolyl complex 33 (Section 3.01.3.2) with COS afforded the dinuclear complex 145 whose structure was determined crystallographically.36 Other products, not involving boron-sulfur heterocycles and hence outside the scope of this discussion, were obtained via the treatment of 33 with different sulfur reagents such as CS2.36... 

Tricyclic sulfur heterocycles 341 were prepared utilizing an intramolecular [4 + 2] cycloaddition. Heating of allenyl sulfides 340 to 110 °C leads to Diels-Alder products 341 in reasonable yields (Scheme 8.93) [163], Unfortunately, this method does not allow general access to these heterocycles, since a particular substitution pattern of the substrate is required. No reaction occurred with substrates lacking the thioacetal moiety. 

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