Adduct with thiourea

In a second historical paper30a) on cyclic oligoethers, Pedersen mentioned several crystalline dibenzo[l8]crown-6 adducts with thiourea in which the thiourea to crown ratio varied from 12 3 to 6 1 30b). The urea complex was first prepared in 1981 by the addition of ether to a homogeneous solution of [18]crown-6 and urea in a 1 2 methanol/chloroform mixture31). Recrystallization from methanol/ethylacetate yielded the analytically pure 5 1 complex with a melting point of 148-150 °C. An X-ray analysis at — 125 °C 31) revealed a crystalline solid with a 5 1 urea/host ratio containing 2 1 complexes and uncomplexed urea. 

Only a few examples of this class of compounds containing divalent tellurium are known. The aryl tellurium nitrates and perchlorates have been isolated only in the form of their adducts with thiourea, triphenylarsine oxide, or as hetaryl A -oxidcs. 

The use of adducts with thiourea on the branched cyclic fraction is demonstrated in Figure 19. ... 

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). 

Because of the structural requirements of the bielectrophile, fully aromatized heterocycles are usually not readily available by this procedure. The dithiocarbamate (159) reacted with oxalyl chloride to give the substituted thiazolidine-4,5-dione (160) (see Chapter 4.19), and the same reagent reacted with iV-alkylbenzamidine (161) at 100-140 °C to give the 1 -alkyl-2-phenylimidazole-4,5-dione (162) (see Chapter 4.08). Iminochlorides of oxalic acid also react with iV,iV-disubstituted thioureas in this case the 2-dialkylaminothiazolidine-2,4-dione bis-imides are obtained. Thiobenzamide generally forms linear adducts, but 2-thiazolines will form under suitable conditions (70TL3781). Phenyliminooxalic acid dichloride, prepared from oxalic acid, phosphorus pentachloride and aniline in benzene, likewise yielded thiazolidine derivatives on reaction with thioureas (71KGS471). 

There are amines such as A-methylnitroamine, that are too weakly nucleophilic to be able to form covalent adducts with arenediazonium ions. The products of the latter appear to be those of salts ArNJ N(N02)CH3, as found by Baranchik et al. (1957). Amides also appear not to be sufficiently nucleophilic, but thioamides are, as is shown by the reaction of A-phenylthiourea in the presence of NaOH (Scheme 13-12 Nesynov et al., 1970). First a (probably homolytic) phenylation-de-diazoniation takes place, followed by A-coupling. Selenourea also reacts a mixture of products is formed, which indicates a reaction of the same type as with thiourea (Nesynov and Aldokhina, 1976). 

Bifunctional thiourea-catalysed enantioselective Michael reaction has been achieved. The thiourea moiety and an amino group of the catalyst activated a nitroolefin and a 1,3-dicarbonyl compound, respectively afford the Michael adduct with high enantioselectivity.177,178 Thioureas work as one of the most effective and general enantioselective nitro-Mannich reaction and carbonyl cyanation catalyst.179,180... 

Wallis185 examined reactions of dimethyl 2-hexen-4-ynedioate with thioureas and thio-amides and observed addition at C-5 via the sulfur atom of these nucleophiles the adducts often cyclize spontaneously to iminothiazolidinones (equation 80). 

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]. 

A second mechanism of inactivation might be the reaction of sulfur-containing biomolecules with the cis-Pt-DNA monoadducts (product 1 in Fig. 4), which prevents those from rearranging to toxic bifunctional adducts. Supportive for such a mechanism is the observation that GSH can be cross-linked to DNA by cis-Pt (41,41a) and [Pt(en)Cl2] (74), and that cysteine can be cross-linked to d-Guo by cis-Pt (77). Furthermore, cis-Pt-DNA monoadducts can be experimentally quenched with thiourea, which reduces drug toxicity (82, 83). trans-Pt also yields monofunctional adducts after reaction with DNA, and these rearrange somewhat slower than does cis-Pt into bifunctional adducts (41,84), clearly for sterical reasons. The relatively long-living monofunctional adducts react efficiently with GSH and proteins (41 a, 84-86). 

Carboxamides form rather unstable 1 1 adducts with HFA insertion into one N—H bond occurring as with urea 202). Addition of another molecule of HFA can only be effected by salt formation with pyridine. The addition is reversible. A stable product 125a is obtained from urea in the presence of acetic acid anhydride 257). Thiourea forms the corresponding oxadiazin-thione 125b with HFA (257). 

A . The estimated enthalpies of dissociation (9-15 kcal/mol) for the phos-phinocopper(I) iodide complexes may be compared to values for SO2 adducts with 1 (4-19 kcal/mol) , NCS (2-4 kcal/mol) , thiourea (13 kcal/mol) , and a variety of alkyl and aryl amines (17-23 kcal/mol) . Organic sulfides, ethers, and alcohols form much weaker complexes with S02 . Weak SO2 interactions with coordinated halides (especially Cl) may be involved in certain other systems such as ZrCl(-S02 and BCl3-S02 ° . ... 

Sulfur-based Cr coordination compounds include a series of dithiocarbamates of the type [Cr(S2CNR2)2] (R = Me, Et or R2 = C4H8), which are antiferromagnetically coupled. The diethyl-substituted compound is an S-bridged dimer, making chromium five-coordinate. Square-planar Cr coordinated by sulfur occurs in the violet [NEt4]2[Cr(S2C2H4)2]. Finally, Thiourea and its derivatives form adducts with Cr halides, which are similar to the adducts with O-donors mentioned above. 

Most of the complexes have well defined melting points. They appear to be monomeric in solution . An interesting method for the preparation of thiazolidine-2-thione complexes of aryl tellurium trichlorides is the addition of the tellurium compound to a melt of the ligand kept at 110°. Complexes with 1 1, 1 2, and 1 4 stoichiometries (Te-compound ligand) were obtained after recrystallization from dry methanol. Phenyl tellurium trichloride complexes with thiourea appear to form only when an organic solvent is used as the reaction medium in aqueous media the trichloride is reduced to the monochloride that is isolated as the thiourea adduct . 

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. 

Extractive Crystallization. Extractive crystallization is a new process whereby the desired component in a mixture is made to form an adduct, the adduct is crystallized out, and the desired component is then recovered. Urea forms such adducts with straight-chain organic compounds, and thiourea forms adducts with branched-chain and ring compounds. A review of the process has been published by Kobe and Domask (45). 

An improvement in the synthesis of the chloride Bii2CI 4, based on crystallization from a reduced KCl-BiCU melt, has been reported, together with new X-ray diffraction data. Bismuth(iii) chloride forms a 1 1 adduct with SnCl2, ° and a structure determination for the thiourea adduct 3BiCl3,7SC(NH2)2 shows the presence of the dinuclear cation [Bi2Cl4(tu)6] and the anion [BiCl5(tu)] all bismuth atoms are in octahedral co-ordination.Stability constants for all... 

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