Carbodiimide from thioureas

N 0 Me 0 From hydroxymethyl polystyrene by treatment with COClj, HjNNHCOjMe and NBS or Cl,.2i Mitsunobu reactions esters from carboxylic acids and alcohols lactones from hydroxy acids A/-aUcylation of phthalimides, a-alkylation of cyanoacetate carbodiimides from thioureas. ... 

Carbodiimides from Thioureas. Conversion of Niff-disubstituted thioureas into carbodiimides can be effected by treatment with (1) and 2 equiv of base (eq 8). ... 

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 alkyl-, alky laryl- and diarylcarbodiimides are the diimides derived from carbon dioxide, however, no direct formation of carbodiimides from amines and carbon dioxide is known. Interestingly, carbodiimides can be obtained from amines and carbon dioxide via a switteri-onic titanium complex (see Section 2.2.8). The major starting materials for the synthesis of carbodiimides are isocyanates, 1,3-disubstituted ureas or 1,3-disubstituted thioureas. The synthesis of isocyanates requires the use of the toxic carbonyl chloride or its oligomers. A book on the synthesis and reactions of isocyanates appeared in 1996. ... 

Similarly, pyrido[2,1 -b]-1,3,4-thiadiazolium-2-amenates are obtained by cyclization of carbodiimides, generated in situ, from thioureas. ... 

High yields of sensitive carbodiimides can be obtained from thioureas under mild conditions with cyanuric diloride and triethylamine and also with quinones Carbodiimidium salts have been introduced as novel reagents and used successfully for the preparation from alcohols of iodides, including sterically hindered compounds... 

The syntheses of substituted 5-aminotetrazoles 228, using azide ions for assembling the tetrazole scaffold, can be divided into two different approaches. The first approach is the addition of sodium azide to car-bodiimides 222 [156,157] or cyanamides 223 [158-161]. The second approach is the nucleophilic substitution of a chlorine in a-chloroformamidines 224 [162], the nucleophilic substitution of benzotriazole in (benzotria-zolyl)carboximidamides 225 [163], the nucleophilic substitution of the sxflfite anion in aminoiminomethanesulfonic acids 226 [164] and the nucleophilic substitution of sulfur from thioureas 227 in the presence of mercury [165] or lead [ 166-169] salts in the presence of an azide ion (Scheme 43). In this chapter, the main focus is on the addition of azides to carbodiimides 222 to form substituted 5-aminotetrazoles 228. 

Unsym. carbodiimides from isothiocyanates and amines via thioureas and isothioureas s. 18, 555 RN G NR ... 

General procedure. Carbodiimides from ureas or thioureas [1262] Equimolar amounts of urea or thiourea, tetrachloromethane, triethylamine, and triphenylphosphine (in... 

Alkyl- and aryl carbodiimides can be prepared under mild conditions from thioureas with diethyl azodicarboxylate/triphenylphosphine (Mitsunobu reagent), typically in yields of around 80% the by-products are triphenylphosphine sulfide and diethyl hydrazodicarboxylate [1278]. The active intermediate in this system is the betaine 1739, which is formed from diethyl azodicarboxylate (DEAD) and triphenylphosphine. Driven by its charge distribution and its chalcogenophilicity, 1739 reacts with the thiourea 1740 to form the P,S bond in 1741. This energy-rich molecule stabilizes by decomposition into three molecules, namely the two byproducts, triphenylphosphine sulfide and diethyl hydrazodicarboxylate, and the desired carbodiimide 1699. Diphenylcarbodiimide 1699 (R = R = Ph) was prepared from N,N -diphenylthiourea 1740 (R = R = Ph) with DEAD and triphenylphosphine in 65% yield [1278]. 

Thioureas are most commonly prepared from reaction of isothiocyanates with amines. Also there are some reports on reactions of anime or carbodiimides with several thionating reagents. AA -Disubstituted thioureas bearing double NH groups have been developed as sensors, and as catalysts because of their hydrogen bonding ability. A,A -Disubstituted thiourea-linked sugar chains have been prepared by the reaction of isothiocyanate with amine. 

Chloro-l-methylpyridinium iodide (683) functions as an important mediator in a variety of different reactions. Esters are formed in high yield from acids and alcohols when reacted with one equivalent of (683) in the presence of two equivalents of triethylamine (Scheme 158) (75CL1045). cv-Hydroxy acids are lactonized under similar conditions (76CL49). The pyridinium salt (683) will also convert thioureas into carbodiimides (77CL575) and pyridine-2-thiones to pyridyl sulfides (75CL1159). 

Isothioureas can be prepared on insoluble supports by S-alkylation or S-arylation of thioureas (Entry 7, Table 14.6). Further methods for the preparation of isothioureas on insoluble supports include the N-alkylation of polystyrene-bound, A/,/V -di(alkoxy-carbonyl)isothioureas with aliphatic alcohols by Mitsunobu reaction (Entry 7, Table 14.6) and the addition of thiols to resin-bound carbodiimides [7]. Resin-bound dithio-carbamates, which can easily be prepared from Merrifield resin, carbon disulfide, and amines [76], react with phosgene to yield chlorothioformamidines, which can be converted into isothioureas by treatment with amines (Entry 8, Table 14.6). The conversion of support-bound a-amino acids into thioureas can be accompanied by the release of thiohydantoins into solution (see Section 15.9). The rate of this cyclization depends, however, on the type of linker used and on the nucleophilicity of the intermediate thiourea. 

A spin labeled carbodiimide derivative 8 is synthesized from the thiourea 7 and HgO. ... 

Sheehan and Hlavka used benzenesulfonyl chloride and aqueous potassium carbonate to synthesize several N-alkyl-N -(aminoalkyl)carbodiimides 14 from the corresponding thioureas 13. 

Dicarbodiimides have not gained the same prominence as diisocyanates as monomers for addition polymers. Dicarbodiimides are obtained from difunctional precursors, such as bis-thioureas. Another synthetic method is the conversion of diisocyanates with iminophosphoranes. The reaction can be condncted stepwise to give an isocyanato-carbodiimide as an intermediate. 

When carbodiimides are generated in the proximity to suitably substituted OH, SH, or NHR groups, subsequent cyclization can give rise to the formation of heterocycles. This reaction is used to synthesize heterocycles 602 from ortho substituted thioureas 601 (X = O, S, NH).562... 

Carbodiimides with aliphatic ester substituents 5 are also obtained in moderate yields from the corresponding thioureas using carbonyl chloride in the presence of triethyl amine to affect the desulfurization. The ester carbodiimides have to be reacted immediately, because polymerization occurs after several hours. 

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