From thioureas

Synthesis. - Hantzsch s Synthesis (Type A S—C—N + C-C) From thioureas. Starting from thioureas, the following compounds have been obtained 2-amino-4-(4-benzyloxyphenyl)thiazoles, 2-(2-amino-5-hydroxythiazol-4-yl)-1 -(4-chloro-3-methylphenyl)ethanone, 2-benzylidenehydrazino-4-( 1,5 -di- 

4-fluoroaryl-thiazoles, 4-substituted 2-aminothiazoles, and 2-amino-4-aryl-thiazoles. 5-Acyl-2-aminothiazoles are also prepared by cleavage of the S-S bond of disulphidocarbamidines, H2NC(=NH)SSC(=NH)NH2, and reaction with /3-diketones.  

Synthesis from thioamides. Compounds prepared using thioamides include 4-(4-chlorophenyl)-2-[4-(hydroxy or acyl)phenyl] thiazol-5-ylacetic acids,2-(hydroxyphenyl)thiazole-4-carboxylic acids and derivatives, and substituted 

5-triarylthiazoles. From HC(S)NH2 and XCH2C0(CH2)30C0Me (X = halo) are formed 5-(2-hydroxyethyl)-4-methylthiazole as the major product and 4-(3-hydroxypropyl)thiazole as a by-product. Also noted are 2,4- 

The reaction of the thiourea 1 with methanesulfonyl chloride in the presence of triethyl-amine and DMPA in methylenechloride at 0 °C affords an 86 % yield of the enyne carbo-diimide 2.  

3-bis-(2-vinyloxyethyl)thiourea is converted into N,N -bis-(2-vinyloxy)ethyl-carbodiimide using HgO in methylene chloride.  

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A new method of synthesizing 2-aminothiazoles from thiourea and ketones has been developed by Dodson (225, 261, 280). It was improved by King and Lavacek (328) and later taken up by several other workers (328, 779, 798) (Method B). 

TABLE U-12. 2-AMINOTHIAZOLES FROM THIOUREA AND -HALOACET-ALDEHYDE AND DERIVATIVES... 

Aminolhtazoles were synthetized from thiourea by three methods Method A, from a-haloketones or aldehydes designated as (Cl) or (Br) Method B, from ketones and iodine (fj) or bromine (Btj) Method C, from iodomercuriketones. Method D consists in condensing ketones with cyanamid and sulfur. 

TABLE 11-40. 2.4-DIAMINOTHIAZOLE DERIVATIVES FROM THIOUREA AND a -H ALOGENONITRILES... 

Furium. N[4-(5-Nitro-2-furanyl)-2-thia2olyl]acetamide, has demonstrated activity against baciUi and pathogenic enterobacteria (24). The product, prepared from thiourea and 2-bromo-l-(5-nitro-2-furanyl)ethanone followed by acetylation of the intermediate aminothia2ole with acetic anhydride in pyridine (25), is marketed in several countries for both human and veterinary use. 

Another entry into the anti ulcer sweepstakes is etinfidine (50). It is synthesized by displacement of halide from 4-chloromethyl-5-methylimidazole (4 ) with substituted thiol The latter is itself made from thiourea analogue by an addition-elimination reaction with cysteamine 52. °... 

Moreau and co-workers have also prepared (ll ,2K)-l,2-diaminocyclo-hexane amino-urea and thiourea derivatives [43]. Diphenylethylenediamine-substituted monothioureas are more stable than the cyclohexyldiamine counterpart, but they can also rearrange to guanidine derivatives, especially at high temperature or in the presence of metal [43]. Under the same conditions, thioureas also rearrange to guanidines in the presence of amines. Selective formation of substituted guanidines from thiourea derivatives of diaminocy-clohexane or diphenylethylenediamine were also reported in a recent paper from Ishikawa [44]. 

Preparation of guanidine from thioureas has been carried out. There are many ways to synthesize guanidines. Converting thioures and isothiourea moieties into guanidine is one of the most popular methods. 

Common synthesis of disulfonium dications involves formation of a S-S bond by oxidative coupling of two sulfide moieties. Involving for oxidative generation of S-S bond, thiocarbonyl compounds can lead to new-type dications containing disulfide moieties between two positively charged fragments. There are several disulfide dications of this type derived from thioureas, thiocarbon-ates and thioketones as well as selenium derivatives.137 148... 

The current state-of-the-art CBD process for CdS consists of cadmium ions, thiourea, and ammonia. The deposition of a uniform CBD CdS thin film occurs because of a chemical reaction of controlled sulfur and cadmium ions in the alkaline solution. The slow release of sulfur from thiourea via decomposition and slow release of Cd2+ ions from CdfNI I3)2 allow the following chemical reactions ... 

As expected, other carriers of NO+ such as nitrosamines55, alkyl nitrites56 and a nitrososulphonamide57 will also generate the S-nitrososulphon i urn ion from thiourea. 

Carbodiimides are rapidly and conveniently obtained from thioureas (Table 10.14) [19], whereas 2-amino- and 2-hydroxyphenylthioureas are oxidatively cyclized to benzimidazoles and benzoxazoles, respectively (Scheme 10.2). 

The reaction of thiourea derivatives with a metal complex to form NHC complexes is a combination of the NHC formation from thioureas with potassium or sodium [Eq. (23)] and the cleavage of electron rich olefins. For example, a lO-S-3-tetraazapentalene derivative is cleaved by Pd(PPh3)4 and [(Ph3P)3RhCl], respectively [Eq. (35)]. Other substitution patterns in the carbene precursor, including selenium instead of sulfur can also be used. ... 

Scheme 63). The alternative structure (403) for the final product should also be considered in the light of the structural revision of the adduct obtained from thiourea and DMAD. ... 

Other examples this type of quinazoline synthesis include the formation of the thione analog 752, by displacement of bromine from thiourea 751 <2003ARK(x)434>, and the imino compound 754, which could be formed by heating the guanidine derivative 753 in DMF, without the need for any added base <2005RJ01071>. 

Typically, thioxonium salts (32) are stable compounds, and the deprotonation is performed at low temperatures. This method has been used to synthesize reactive thiocarbonyl yhdes as well as stable and isolable ones (56-60). Arduengo and Burgess (3) prepared differently substituted thiocarbonyl ylides from thiourea derivatives, and in the case of 33, the structure has been established by X-ray crystallography. 

Unfortunately, it is nontrivial to distinguish reliably between the complex-decomposition and sulphide-formation mechanisms. For example, in the study of PbS (as a precipitate) formation from thiourea [47], the two main results used to support complex decomposition were (a) very little sulphide was formed in alkaline solutions of thiourea and (b) addition of PbS powder catalyzed the reaction, seen by the disappearance of the induction time for precipitation and more rapid PbS formation when PbS was added at the start of the reaction. However, these results would also be obtained in a free-anion mechanism, for the following reasons ... 

Some specific properties of ZnS films grown from thiourea/ammonia/hydrazine baths, sometimes with added compounds, are given next. 

Triethanolamine was also used as a complexant to deposit these films from thiourea baths [18]. As with the previous study, there was a maximum Hg content in the bath (0.05 mole fraction—absolute concentrations were not given), which led to a 0.18 Hg mole fraction in the films, above which, although films were formed, the Hg content decreased, also explained by rapid precipitation of HgS in the solution. X-ray diffraction showed the formation of a single phase, up to a Hg content (in the bath) of 0.15, and two-phase formation at higher concentrations. The optical bandgap dropped from 2.4 eV (pure CdS) to 1.76 eV (0.05 Hg in bath. 

Isothioureas similarly give, in neutral media, the corresponding 3-alkylthio-5-amino-l,2,4-thiadiazoles (65) in yields exceeding 70%.84"86 However, the attempted preparation of the parent 5-amino-3-mercap-to-l,2,4-thiadiazole from thiourea or dithioformamidine by this route yielded only intractable mixtures.85... 

Cyanoethylthiouronium hydrochloride (3) has been prepared by Bauer and Welsh from thiourea hydrochloride and acrylonitrile in a 61% yield on a 20-g scale.3 It has also been prepared by Bauer and Welsh3 and by Traut, et al.4 using a procedure similar to the one described here on a 17.5-g and 25-g scale, respectively. Both procedures describe the reaction being carried out at refluxing solvent temperatures. These procedures were not reproducible and applicable as described for larger scale preparations. More importantly, they were not safe, as the reaction of thiourea with 2-chloropropionitrile is very exothermic. The procedure described here allows for the safe and reproducible preparation of 2-cyanoethylthiouronium hydrochloride on a scale even 10-fold larger than the one described. 

Thiourea masks Cu2+ by reducing it to Cu+ and complexing the Cu+. Copper can be liberated from thiourea by oxidation with H202. Selectivity afforded by masking, demasking, and pH control allows individual components of complex mixtures of metal ions to be analyzed by EDTA titration. 

Formation of imidazoles from thiourea derivatives has been limited largely to the 2-alkylthio or 2-aralkylthio-substituted rings (unsubstituted 2-mercaptoimidazoles will be classified as 4-imidazoline-2-thiones in this review). 

Alkyl (or aryl) 5-aminotetrazoles (38) can be prepared either from thioureas by reaction with sodium azide in the presence of lead carbonate89 or from 2-thiopseudourea hydriodides by reaction with sodium azide.70... 

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