Allyl thiourea

When treated with alcoholic solution of ammonia, it yields thio-sinamine (allyl thiourea), of the formula C3H5. NH. CS. NHj. This body melts at 74°. The formation of this body forms the basis for a method of its determination, which, with other methods, will be found fully described under Oil of Mustard (Vol. I, p. 474). 

Peroxy radicals are known to be formed on exposure of irradiated PMMA to O. Thus in the presence of some oxidative degradation would take place but its nature is most likely different from that of the degradation in the absence of Oj. The addition of benzene and many free radical scavengers e.g., allyl thiourea) also protects PMMA against radiation-induced degradation. PMMA undergoes grafting by direct irradiation, post-irradiation by trapped free radicals or on irradiation in a blend [Chapiro, 1962]. 

More recently, the microwave copolymerization of dibutyltin maleate (DBTM) and allyl thiourea was investigated, under conditions specified above to produce organo-tin copolymers [46]. Under microwave irradiation, the copolymers could be synthesized without and in the presence of free radical initiator however, in the presence of initiator the conversion of monomers was slightly higher to reach ca. 35 %. Without using any initiator, the monomers did not copolymerize by conventional heating within 7 h at all. The copolymers were applied for thermal stabilization of PVC. The thermal stability was increased from 180 °C for neat PVC to above 240 °C for PVC modified with the organo-tin copolymers [46]. 

Allyl thiourea ( CnHgNsS ) + 3-Naphthol ( C,oHsO ) Kofler and Btandstatter, 1942... 

The copolymerization of N,N-dimethylaminoethyl methacrylate with allyl thiourea was performed under microwave irradiation (domestic microwave oven) by Lu et al. (2005). The influence of reaction time and nucrowave power on the copolymerization was studied. Copper was coordinated to this polymer by microwave irradiation. This polymer-copper system was used as heterogeneorrs catalyst for the polymerization of methyl methacrylate. 

N-substituted compounds such as phenyl-, acetyl- or allyl-thiourea in 0.5 to 1% concentration give composites with excellent color stability. However, the biocompatibility of these compounds has not been established. 

N-monosubstituted thioureas also react with a-haJoacids or esters to give stable compounds of type 126, in which R is aryl or acyl. When R is alkyl such as an allyl group (85), isomer 125 is formed (Scheme 60). 

In contrast to the above additions A-allyl- and substituted A-allyl-amides, -urethanes, -ureas and -thioureas undergo intramolecular cyclization only in 6(3-96% sulfuric acid to give the corresponding oxazolinium and thiazolinium salts. Treatment of these cations with base yields 2-oxazolines and 2-thiazolines in moderate to good yields. The reaction is illustrated by the conversion of A-2-phenylallylacetamide (342) into 2,5-dimethyl-5-phenyl-2-oxazoline (343) in 70% yield 70JOC3768) (see also Chapter 4.19). 

In 450 cc of methanol is added 47 grams of sodium metal and the mixture allowed to completely react to form a methanol solution of sodium methoxide. The methanol solution of sodium methoxide is then cooled to 60°C and 68 grams of thiourea which has been thoroughly dried is added with stirring until a uniform solution is formed. Thereafter, 157 grams of diethyl allyl-(1-methylbutyl)malonate is added to the solution of the sodio derivative of thiourea at a temperature of 55°C and the condensation reaction mixture maintained at the said temperature for 24 hours. Methyl alcohol is removed under vacuum during the course of the reaction while maintaining a temperature of 55°C. 

Thiourea was used as stabilising agent for zerovalent Pd species [117]. The Pd-thiourea (H2NCSNH2) catalysed carbonylation of terminal alkynes and allylic alcohols has been described by Chiusoh [118]. More recently, Pd-thiourea-catalysed carbonylative annulation was studied. The reaction proceeds between alkynes, iodophenol acetates and carbon monoxide, in the presence of dppp, thiourea (H2NCSNH2) and base at 40 °C. Flavones have been obtained in good yields (Scheme 30) [119]. 

Even if organocatalysis is a common activation process in biological transformations, this concept has only recently been developed for chemical applications. During the last decade, achiral ureas and thioureas have been used in allylation reactions [146], the Bayhs-Hillman reaction [147] and the Claisen rearrangement [148]. Chiral organocatalysis can be achieved with optically active ureas and thioureas for asymmetric C - C bond-forming reactions such as the Strecker reaction (Sect. 5.1), Mannich reactions (Sect. 5.2), phosphorylation reactions (Sect. 5.3), Michael reactions (Sect. 5.4) and Diels-Alder cyclisations (Sect. 5.6). Finally, deprotonated chiral thioureas were used as chiral bases (Sect. 5.7). 

New organocatalysts prepared by the Jacobsen group showed that alkylation of the final amide bond increased the enantioselection (Scheme 38, compare R2 = Me, 98% ee to R2 = H, 91% ee). Thus, the reaction performed with N-allyl benzaldimine and with the dimethylamide-ending thiourea (Scheme 38 with Ri = R2 = Me) gave up to 99% ee. This compound is a structural analogue of the urea depicted in Scheme 36 [148,152,154]. 

Both the ureas and thioureas are highly suitable organocatalysts for the asymmetric Strecker synthesis. For example, the thiourea function was replaced by an urea function (note the opposite configurations). The organocatalysts thus obtained showed similar activity and slightly higher enantioselec-tivities with N-allyl benzaldimine (Scheme 39,74% yield with 95% ee for Ri = Bn and R2 = H). Once again, better enantioselectivity (up to 99% ee) was at-... 

Various thiourea ligands have been used in the synthesis of mixed ligand complexes. A series of complexes [NiQ2L2] (HQ = ethylacetoacetate, L = thiourea, allyl-, benzoyl-, methyl-, diphenyl-thiourea) have been prepared. The complexes are all paramagnetic (/i = 3.02-3.27/iB) and have been assigned tra 5-octahedral structures.1014... 

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

Allylic bromides reacted with KSCN/Si02 and BnNH30Ac/Al203 in one-pot gives the corresponding thioureas. Reactions of crotyl bromide with a series of alkylammonium acetates, with the exception of tert-butylammonium acetate, results in the corresponding thioureas (Scheme 49).130... 

Hydrogen-bond donors have the ability to enhance the selectivities and rates of organic reactions. Examples of catalytic active hydrogen-bond donor additives are urea derivatives, thiourea derivatives (Scheme 10, Tables 12 and 13) as well as diols (Table 14). The urea derivative 7 (Scheme 9) increases the stereoselectivity in radical allylation reactions of several sulphoxides (Scheme 10)171. The modest increase in selectivity was comparable to the effects exerted by protic solvents (such as CF3CH2OH) or traditional Lewis acids like ZnBr2172. It was mentioned that the major component of the catalytic effect may be the steric shielding of one face of the intermediate radical by the complex-bound urea derivative. 

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. 

Berkessel and co-workers have demonstrated the utility of the bifunctional cyclohexane-diamine catalysts in the dynamic kinetic resolution of azalactones (Schemes 60 and 61) [111, 112]. The authors proposed that the urea/thiourea moiety of the catalyst coordinates and activates the electrophilic azlactone. The allyl alcohol nucleophilicity is increased due to the Brpnsted base interaction with the tertiary amine of the catalyst. 

Scheme 6.23 Claisen rearrangement of a 2-alkoxycarbonyl substituted allyl vinyl ether in the presence of thiourea derivative 9.

Cyclic thioureas such as 2-thiouracil 1118 (R = H), its 6-methyl 1118 (R = Me) and 6-propyl derivatives 1118 (R = Pr), as well as thiobarbital 1119 are effective agents against hyperthyroidism, while thiamylal 1120 is used as an anesthetic. A large number of barbituric acid derivatives have hypnotic or sedative effects, and allobarbital 1121 (R = R = allyl), aprobarbital 1121 (R = allyl, R = r-Pr), cyclobarbital 1121 (R = Et, R = 1-cyclohexenyl), pentobarbital 1121 (R = Et, R = 2-pentyl), phenobarbital 1121 (R = Et, R = Ph), propallyonal 1121 (R = isopropyl, R = 2-bromoallyl), and secobarbital 1121 (R = allyl, R = 2-pentyl) are all examples of N-unsubstituted barbiturates, while hexobarbital 1122 represents an N-methylated derivative. 

The asymmetric alcoholytic ring opening of 4-substituted-2-phenyl-4,5-dihydro-l,3-oxazin-6-ones proved to be a efficient method for the preparation of enatiomerically pure /3-amino acid derivatives <2005AGE7466>. Treatment of 2,4-diphenyl-4,5-dihydro-l,3-oxazin-6-one 208 in the presence of the bifunctional chiral thiourea catalyst 211 resulted in formation of an enantiomerically enriched mixture of the unchanged oxazinone (iJ)-208 and allyl (4)-3-benzoyl-amino-3-phenylpropanoate 209. The resolved material (iJ)-208 and the product 209 could easily be separated by a selective hydrolytic procedure that converted oxazinone (iJ)-208 quantitatively into the insoluble iV-benzoyl /3-amino acid 210 (Scheme 37). 

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