Urea, reaction with conjugated acids

Another cycloaddition approach utilized the reaction of the alkene moiety of a conjugated acid such as 4-methyl-2-pentenoic acid with urea to give uracil 2.170. ... 

Figure 15 Conjugation of a carboxylic add and an amine using the carbodiimide method. The carbodiimide activates the carboxyhc acid to speed up the reaction to the amine. Carbodiimides can be used with nonpolar or polar solvents, including water. Undesirable urea complexes may form as by-products. Details of the reaction are given in Table 3...

Copper Phthalocyanine. 6CgH C2N) Nj Cu solid d 1.59. A blue pigment deriv of org pigments having as a structural unit four isoindole groups, (CgH )C2N, linked by four N atoms so as to form a conjugated chain. It is extremely stable to Ugh acids, alkalies and heat. Can be prepd by reaction of phthalic anhydride, urea cuprous chloride at ca 200° or by reaction of o-chlorocyanobenzene with cuprous cyanide Cu pdr. Has been used in enamels, linoleum, plastics, rubber goods, etc. (Refs 2 3)-The uses of phthalocyanines in propints are discussed in Ref 4 Refs l)Beil - not found under Phthalcyanin or under 6 32 16 8 ° Hackh s (1944), 654 ... 

Another important asymmetric epoxidation of a conjugated systems is the reaction of alkenes with polyleucine, DBU and urea H2O2, giving an epoxy-carbonyl compound with good enantioselectivity. The hydroperoxide anion epoxidation of conjugated carbonyl compounds with a polyamino acid, such as poly-L-alanine or poly-L-leucine is known as the Julia—Colonna epoxidation Epoxidation of conjugated ketones to give nonracemic epoxy-ketones was done with aq. NaOCl and a Cinchona alkaloid derivative as catalyst. A triphasic phase-transfer catalysis protocol has also been developed. p-Peptides have been used as catalysts in this reaction. ... 

Metal-mediated approaches to the synthesis of imidazoles have been reported. PaUadium(ll)-catalyzed intermolecular 1,2-diamination of conjugated dienes with ureas led to 4-alk enyl-2-imidazolones in good yields rmder mild conditions <05JA7308>. Palladium-catalyzed cyclization of O-pentafluorobenzoylamidoximes 74 furnished l-benzyl-2-substituted-4-methylimidazoles 75 <050L609>. Direct copper(I)-chloride mediated reaction of nitriles 76 with a-amino acetals 77 followed by acidic reaction led to a variety of 2-substituted imidazoles 78 <05TL8369>. 

Proline derivatives possess a prominent position among the aminocatalysts utilised for carbonyl activation. In combination with the readily tunable properties of the (thio)urea functionality for electrophile activation, the development of bifunctional chiral pyrrolidine-based (thio)ureas was a rational extension. In 2006, Tang and coworkers reported thiourea 55 that can catalyse the conjugate addition reaction between cyclohexanone and nitroalkenes (Scheme 19.63). In the presence of 20 mol% of chiral thiourea 55 and butyric acid as the cocatalyst, the q -products were delivered in high yields (up to 98%) and in excellent diastereo- (up to >99 1 dr) and enan-tioselectivities (up to 98% enantiomeric excess). In addition to aromatic nitroalkenes, aliphatic nitroalkenes were also tolerated, but required a long reaction time (6 days). 

The important tetramethrin alcohol 323 (Reaction scheme 236) is simply made from butadiene and maleic anhydride, and then rearranged to the conjugated dicarboxyhc acid 324, selectively catalyzed by carbonyls of transition metals Uke Pd, Rh and ruthenium. Imidation with urea and hydroxymethylation produces the final product 323 [688, 689]. 

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