Formation from thioureas

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. ... 

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 ... 

SCE formation probably derives from neither the mutagenic nor cytotoxic cls-DDP lesion. The non-mutagenlc trans-DPP can form SCE s. Immediate thiourea can only block SCE formation at very low cls-DDP doses and delaying thiourea allows almost total escape of SCE formation from thiourea blockade. DNA monoadduct formation may Induce SCE formation. What little effect thiourea does have on SCE formation may derive from thiourea s binding of unreacted. Intracellular Pt prior to Its binding to DNA at all. 

The equilibrium constant for its formation from thiourea and nitrous acid has been... 

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]. 

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... 

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>. 

Thermodynamic analyses of metal sulphide formation from thiosulphate [52] and thiourea [53] and metal selenide formation from selenosulphate [13,54]... 

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. 

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). 

The chemistry leading to the formation of s-triazines from thioureas has been of considerable interest historically, and is well summarized in a monograph by Smolin and Rapoport249 thus the newer or less common aspects of these reactions will be dealt with here. 

A myriad of types of fused-ring pyrimidines derived from thioureas have been reported in the literature. For example, Howard and Lindsey387 reported the [l,3]-dithiino[5,4-d]pyrimidine ring system 223, and other workers made the octahydrobenzo[6]thieno[2,3-d]pyrimidirie 224 in 90% yield.388 The formation of both of these products was via a base-promoted condensation of a thiourea with a carbethoxy group however, in the former case the reaction was intermolecular and in the latter, intramolecular. Other unusual fused systems of this type have... 

Oligothioureas have been prepared on cross-linked polystyrene from Boc-pro-tected oaminoisothiocyanates, which were synthesized in solution from symmetric diamines [258]. The formation of thioureas from support-bound amines and isothiocyanates is a rather sluggish reaction (e.g. 3 d, 45 °C, mean coupling yield 90% [258]), and only short oligomers can be prepared using this strategy. 

Formation of thiourea linkages from isothiocyanates and e-amino groups of lysine residues in proteins... 

Condensations. Alumina promotes the formation of a-hydroxyphosphonate esters from aromatic aldehydes and dialkyl phosphonates, and the adducts are converted to a-aminophosphonate esters on reaction with ammonia. A solvent-free synthesis of a-nitro ketones comprises mixing nitroalkanes, aldehydes, and neutral alumina and oxidizing the adducts with wet, alumina-supported CrOj (15 examples, 68-86%). The Knoevenagel reaction, the Michael addition of nitromethane to gcm-diactivated alkenes, and the formation of iminothiazolines from thioureas and a-halo ketones are readily effected with alumina under microwave irradiation. 

Figure 34. Hydrogen-bonded layer in 2(C2Hs)4N HC02-2(NH2)2CS HC02H (2.11) formed by ribbons constructed from thiourea dimers and protonated formate trimers. Broken lines represent hydrogen bonds.

Figure 41. Projection diagram showing a hydrogen-bonded layer constructed from (thiourea-formate)2 tetramers in the crystal structure of (C2H5)4N HC02-(NH2)2 CS H2O (2.10). Broken lines represent hydrogen bonds.

Mercapto-l,3-dimethyl-IcP-2-one formation from the 4-chloride in high yield was accomplished on heating with thiourea in alcohol (94KG1071). 

The elimination of a hydrogen sulfide molecule from thioureas by the use of diethyl azodiformate (78) is also initiated by the same S-N bond formation. 

Thiourea is an efficient catalyst for the nitrosation of morpholine and the diazotization of aniline. In the former case the efficiency of thiourea SCN" Br as catalysts lies in the ratio 4200 240 1. For thiourea this reflects the large equilibrium constant for the formation of the ON—S= ion from thiourea, rather than a large rate constant for the attack of the... 

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