Thioureas symmetrical

In 1874 Claus [5] reported that thiourea reacts with ethyl iodide or bromide to give compounds whose structures were first suggested to be pseudothioureas by Bernthsen and Klinger [6] (Eq. 3). In place of thiourea, symmetrical... 

The symmetrical disubstituted thioureas such as 137 do not give a thiazolic ring (Scheme 66), but give compounds of type 138 or 139, which are derived from the tautomer imino form of the 2-aminothiazole (86). 

Fluorophenyl isothiocyanate [1544-68-91 M 153.2, m 24-26 , 26-27 , b 66 /2mm, 215 /atm, 228 /760mm, n 1.6116. Likely impurity is the symmetrical thiourea. Dissolve the isothiocyanate in dry CHCI3, filter and distil the residue in a vacuum. It can also be steam distd, the oily layer separated, dried over CaCl2 and distilled in vacuo. Bis-(4-fluorophenyl)thiourea has m 145 (from aq EtOH). [Browne and Dyson J Chem Soc 3285 1931 Buu Hoi et al. J Chem Soc 1573 1955 Olander Org Synth Coll Vol I 448 1941 ]. 

Salts of dithiocarbamic acid can be prepared by the addition of primary or secondary amines to carbon disulfide. This reaction is similar to 16-9. Hydrogen sulfide can be eliminated from the product, directly or indirectly, to give isothiocyanates (RNCS). Isothiocyanates can be obtained directly by the reaction of primary amines and CS2 in pyridine in the presence of DCC. ° In the presence of diphenyl phosphite and pyridine, primary amines add to CO2 and to CS2 to give, respectively, symmetrically substituted ureas and thioureas ... 

Chiral amines and diamines are readily available substrates for the synthesis of ligands for transition metal-catalysed reactions since they can easily be transformed into chiral ureas and thioureas. Therefore, several groups have prepared chiral symmetrical ureas and thioureas, dissymmetrical ureas and thioureas, amino-urea and thiourea derivatives. Finally polyureas and non-soluble polythioureas were also prepared and tested as ligands for asymmetric catalysis. 

Treatment of a chiral amine with phosgene is the cheapest way to prepare symmetrical ureas [29]. Nevertheless, due to the toxicity and reactivity of that reagent, it can advantageously be replaced by triphosgene [30] or l,l -carbonyldiimidazole [31-34] or other derivatives such as l,l -carbonyldi-2(lH)-pyridinone [35]. This procedure can be extended to thiophosgene (Scheme 1) and its thio-analogues, such as l,l -thiocarbonyldi-2(lH)-pyridinone to produce thioureas [36] chiral diamines can thus be transformed into the corresponding monoureas or monothioureas. 

Other metals such as iridium have also been combined to chiral sulfur-containing ligands in order to induce the chirality in the hydrosilylation of ketones. Therefore, Lemaire et al. have described the use of several chiral thiourea ligands for the iridium-catalysed hydrosilylation of acetophenone. The best but moderate enantioselectivity (52% ee) was observed with the use of a C2-symmetric monothiourea ligand (Scheme 10.49) while the employment of... 

For molecules with small dipoles, the adsorption region is distributed symmetrically around the potential of the electrocapillary maximum. However, if chemisorption interaction occurs between one end of the dipole (e.g. sulphur in thiourea) and the electrode, the adsorption region is shifted to the negative or positive side of the electrocapillary maximum. 

Reaction of carbon disulfide with primary amines, using MCM-41-TBD (mesoporous MCM-41 silica, TBD l,5,7-triazabicyclo[4.4.0]dec-5-ene) as catalyst, has given symmetrical thioureas under heterogeneous conditions. The MCM-41-TBD could be reused as a catalyst (Scheme 43).123... 

Reaction of carbon disulfide with primary amine hydrochloride in the presence of dimethyl aminopyridine (DMAP) and A,A -dicyclohexylcarbodii-mide (DCC) affords symmetrical thioureas (Scheme 44).124,125... 

Condensations of amine hydrohalides with potassium thiocyanate (KSCN) provide both the primary thioureas and symmetrical 7V,7V -disubstituted thioureas. Selectivity in the product was achieved by changing the concentration of KSCN as shown in the diagram (Scheme 50).131... 

Symmetrically disubstituted thioureas have been synthesized by heating thiourea with aromatic amines or phenylhydrazine under environmentally benign conditions without solvent in a conventional microwave oven (Scheme 54).136... 

The conversion of symmetrical into unsymmetrical thioureas is exemplified by the formation of Af-cyclohexyl-Af -phenylthiourea when yV,iV-diphenyl thiourea is heated with cyclohexylamine and triethylamine in acetonitrile367. Carbonylation of lithium piperidide in the presence of tellurium generates the lithium carbamotellurate 307, which is trapped as the 7V-ethyl carbamotellurate 308 by ethyl bromide368. 

Symmetrical dialkyl and diaryl thioureas have been prepared in generally good yield (60-90%) from the reaction of the amine with thiophosgene, formed in situ from the catalysed reaction of carbon tetrachloride with sodium sulphide [5], Reaction with diamines yields cyclic ureas. 

Alternative precursors for the synthesis of NHCs are thiourea derivatives of type 3. The preparation of such thiones with a symmetrical substitution pattern is achieved by the reaction of a-hydroxyketones like 3-hydroxy-2-butanone with suitable 2-thiones (Fig. 3d) [31] or by reaction of a diamine with thiophosgene [32, 33]. Unsymmetrically substituted thiones 4 possessing a saturated heterocycle have also been described (Fig. 3e) [34, 35]. 

The first step of the catalytic process is the hydrogen bond directed assembly and orientation of the reactants. In this example, the azlactone and methanol form a ternary starting complex with the organocatalyst (Fig. 1) [39]. The pseudo-Lewis acidic thiourea forms two bifurcated, nearly symmetric hydrogen bonds (2.147 A, < (0,H,N) = 155.5° and 2.146A, <(0,H,N) = 155.8°) to the carbonyl oxygen atom of the azlactone. 

A new and convenient synthesis of 1,3,4-thiadiazoles was reported and involved the direct conversion of 1,3,4-oxadiazoles using thiourea as the thionating agent <98SC4611>. Courtois et al. have described an efficient monohydroxyarylation (or alkylation) and symmetrical bis-hydroxyarylation (or alkylation) of 2,5-dimethyl-1,3,4-thiadiazole using LDA and the appropriate carbonyl compound <99SC145>. 

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. 

Symmetrical diphenyl thiourea (thiocarbanilide) (C HjNH CS is a solid, mp 154 0. When heated with concentrated HC1, the compound yields aniline plus phenylisocyanate. Formed by the reaction of aniline and CS2, symmetrical diethylthiourea (C2H5NH)2CS is a solid, mp 77°C. 

The C2-symmetric chiral bis-thiourea catalyst 78 mediated the addition of cyclohexanone to a range of activated aldehydes in the presence of DMAP, or imida-... 

This general reaction can be used for preparing other un-symmetrical thioureas when the desired cyanamides can be obtained. The submitter has also prepared l-methyl-l-(l-naph-thyl)-2-selenourea, m.p. 174-175° with decomposition, and l-ethyl-l-(l-naphthyl)-2-selenourea, m.p. 168-170° with decomposition, by substitution of hydrogen selenide for hydrogen sulfide. 

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