Thioureas basicity

CdCl2 sodium citrate thiourea basic/RT CdS films Water Tomas (1995)... 

Glycosidic thiol groups can be introduced into glycosyl bromides by successive reactions with thiourea and aqueous sodium disulfite (D. Horton, 1963 M. Cemy, 1961, 1963). Such thiols are excellent nucleophiles in weakly basic media and add to electrophilic double bonds, e.g., of maleic esters, to give Michael adducts in high yields. Several chiral amphiphiles have thus been prepared without any need for chromatography (J.-H. Fuhrhop, 1986 A). 

In 1877, Maly (45) discussing formula 34 applied to thiohydantoine found it unable to explain the basic properties of the compound. He preferred a structure in which the -CH2-CO- group would be bonded to only one nitrogen atom. Meyer (46) prepared a monophenyl thiohydantoin (m.p. 178°C) by condensing diloroacetanilide with thiourea and proposed 42 for its structure. 

Hydrogen sulfide reacts with nitriles in the presence of a basic catalyst forming thioamides. A commercial example is its addition to cyanamide with the formation of thiourea [62-56-6]. ... 

The synthesis of 2-substituted pyrimidines from 1,3-dicarbonyl compounds and urea derivatives was first described by Evans2 and was later improved by Hunt, McOmie, and Sayer3 for the preparation of 2-mercapto-4,6-dimethylpyrimidine. Burness4 employed 3-ketobutyraldehyde acetal in this procedure to give 2-mercapto-4-methylpyrimidine. 2-Mercaptopyrimidine has been prepared from 1,1,3,3-tetraethoxypropane and thiourea by variations of this basic method 3 6 6 as well as by the reaction of 2-chloropyrimidine with thiourea 1 or sodium hydrosulfide.8... 

Rieke PC, Bentjen SB (1992) Deposition of cadmium sulfide films by decomposition of thiourea in basic solutions. Chem Mater 5 43-53... 

Figure 12.3 Effect of thiourea on exhaustion of Cl Basic Yellow 21 (12.13) by acrylic fibres [57]...

The main method of crosslinking the homopolymer and copolymer is by use of thioureas, and, as the cure reaction requires basic conditions, an acid acceptor is also added. Litharge, red lead, magnesium oxide and dibasic lead phosphite are commonly used acid acceptors, and the most commonly used thiourea is ethylene thiourea, but this has a tendency to promote mould fouling. 

Heterocyclic rings can be produced from the reaction of a chalcone 203 under basic conditions with urea or thiourea, generating the corresponding diaryl guanidinium structure 204a or 204b as displayed in Scheme 56 by Kidwai and... 

Under basic conditions, A -acridinylmethyl-substituted thiourea 449 placed in the presence of bromoacetonitrile gave rise to the unexpected formation of the spiro[dihydro-acridine-9(10//),2 -(2, 7 -dihydro-3 //-imidazo[l,2-c]thiazol-5 -ylidene-/>-nitrophenyl)amine] 450 in 67% yield. The reaction involved displacement of the bromine atom of... 

The most practical approach is the direct treatment of azolium salts with metal complexes under neutral or basic conditions [39,154-159]. Alternatively, the free carbenes can be generated in the presence of a suitable metal complex by reduction of a carbene precursor, e.g. a thiourea [160]. Stable, uncomplexed imidazoline-2-ylidenes, isolated for the first time in 1991 by Arduengo [161] (for further examples see [162-166]), are also convenient starting materials for the preparation of carbene complexes [167,168]. The corresponding diaminocarbene complexes can be obtained by treatment of the stable diaminocarbenes with transition metal complexes. Finally, at high temperatures many transition metal complexes catalyze the carbon-carbon bond scission of tetraaminoethylenes, forming carbene complexes [169-171]. Examples of such preparations are given in Table 2.8. 

FIGURE 13 Separation of the neutral analytes thiourea (I), benzamide (2), anisole (3), benzophenone (4), and biphenyl (5) using a 240 x 0.1 mm capillary packed with 3 pm Hypersil CEC Basic CIS in micro-LC and voltage-assisted micro-LC mode 1.0MPa of pressure applied to the inlet vial applied voltage as stated in figure mobile phase ACN/50 mM Tris buffer pH 7.8, 8 2 (v/v) cartridge temperature, 20 C Detection, 254 nm Injection hydrodynamic 0.8 MPa/15 s. (Reproduced with permission from reference 67.)... 

Hydroxyl radicals were generated radiolytically in NaO-saturated aqueous solutions of thiourea and tetramethylthiourea. Conductometric detection showed that HO and a dimeric radical cation were produced. The dimeric radical cation is formed by addition of a primary radical to a molecule of thiourea. In basic solution, the dimeric radical cation decays rapidly to a dimeric radical anion, which is formed via neutralization of the cation and subsequent deprotonation of the neutral dimeric radical (Scheme 16). This was not observed in tetramethylurea. These dimeric radical cations of thiourea and tetramethylurea are strong oxidants and readily oxidize the superoxide radical, phenolate ion, and azide ion. 

The authors have also studied the deprotection by less basic nucleophiles such as thiophenolate and iodide. Deprotection by the latter anion may lead to a side-reaction when condensation of the allyl iodide formed with the de-protected phosphorothioate leads to the corresponding S-allyl phosphoroth-ioate. To suppress this side reaction thiourea was used to trap the allyl iodide. 

The acyl-Pictet-Spengler reaction is also catalyzed by chiral thiourea derivative 6 to provide M-acetyl p-carbolines in high enantioselectivities. Notably, thiourea derivatives can activate not only electronically distinct imine derivatives such as N-alkyl and N-Boc imines but also a weakly Lewis basic N-acyhminium ion with high enantioselectivity using a chiral hydrogen bond donor (Scheme 12.4). 

A special case of SNAr is shown in Fig. 20. It actually involves a tandem 8 2-SNAr process on an Ugi adduct containing both an alkyl and an aryl halide. In 99, the acid-derived alkyl halide behaves therefore as a masked nucleophile. Treatment with thiourea (Sn2) forms an intermediate thiouronium salt which, upon basic hydrolysis, releases the required thiolate that undergoes the SnAt process. A library of benzothiazepinones 100 was produced in this way [92]. 

Scheme 6.55 Design principle of amine-functionalized bifunctional thiourea organocatalysts derived from privileged monofunctional thiourea 9 cooperating with an amine base additive (A) and basic bifunctional mode of action of chiral amine...

Tsogoeva and co-workers explored the catalytic potential of pyridyl- and imida-zoyl-containing thiourea derivatives (e.g., thiourea 92 and 93) in the asymmetric model Strecker reactions [157] of N-benzyl- and benzhydryl-protected benzaldi-mine with HCN [258], The observed enantioselectivities were consistently very low (4—14% ee) for all catalyst candidates and were far below synthetically useful levels, while imidazoyl-thiourea 93 was reported to be highly active and displayed 100% conversion (at 7% ee) of the N-benzhydryl-protected benzaldimine (Scheme 6.99). X-ray structure analysis of a pyridyl-thiourea revealed an intramolecular hydrogen-bond between the basic ring nitrogen and one amide proton. This could make this... 

Scheme 6.147 visualizes two proposals for the mechanism of the 131-catalyzed Henry addition of nitromethane to benzaldehyde. In (A), benzaldehyde is achvated by the thiourea moiety through double hydrogen bonding to the carbonyl funchon, while the nitromethane is deprotonated and activated by the basic quinuclidine nitrogen [298] proposal (B), however, based on detailed DFT computations... 

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