Monosubstituted ureas

Michael reaction, A1<9) octalone, 45, 82 N Mono- and N,N disubstitdted UREAS AND THIOUREAS 45, 69 N Monosubstituted thioureas from primary amines and silicon tetra-lsothiocyanate, 45, 69 N Monosubstituted ureas from primary amines and silicon tetraisocyan-ate, 46, 69... 

N-Monosubstituted ureas from primary amines and silicon tetraisocyan-ate, 45, 69... 

The ureidocarbonylation reaction provides access to hydantoins containing diverse substituents in the 1-, 3-, and 5-positions with good selectivities (Table 2) [37]. With monosubstituted ureas, 3-substituted hydantoins are obtained. 

A new microwave-assisted protocol for the generation of diversely substituted 3,4-dihydropyrimidine-5-carboxylic acid esters 40 has been developed by Kappe and co-workers [88, 89] using trimethylsilyl chloride (TMSCl) as a mediator for the Biginelli MCR. This involved the reaction of S-ethyl acetothioacetate or ethyl acetoacetate, an aromatic aldehyde and (monosubstituted) urea or thiourea as building blocks. Also sterically hindered aromatic and heterocyclic aldehydes... 

Symmetrical dialkyl- and diaryl-ureas are formed in 43-78% yields by heating primary amines and ureas in the dry state at 160° or by boiling an aqueous solution of the amine hydrochloride and urea. Urea is converted to ammonium cyanate, which reacts with the amine to give a monosubstituted urea. This compound, in turn, breaks down into an al-kylisocyanate from which the sym-dialkylurea is obtained by the action of more primary amine. By interrupting this process from time to time, phenylurea can be made from aniline and urea in 55% yield. The remainder of the product is syTTz-diphenylurea. ... 

Tiemann rearrangement. Rearrangement of amide oximes (available from nitriles and hydroxyl-amine) to monosubstituted ureas by treatment with benzenesulfonyl chloride and water. 

Monosubstituted ureas are usually sweet although some are tasteless. Urea itself is Bitter. Symmetrical molecules are often Bitter... 

Some 1-aryl-substituted hydantoins have been synthesized by acid-catalyzed condensation of monosubstituted ureas and glyoxal with moderate yields.34... 

Very good yields are almost always obtained by starting with nitro-urea.1154-1157 In these cases the N02NH group is exchanged almost exclusively, so that this method is especially suitable for preparation of monosubstituted ureas and is in many cases superior even to the route from isocyanates.1155... 

Monosubstituted ureas are usually sweet although some are tasteless. 

We have observed that in the reaction of N-monosubstituted ureas with phosphorus pentachloride attack on nitrogen as well as on oxygen occurs, depending upon the substituents attached to nitrogen... 

The reaction is not given by any of the natural amino acids, purines, pyrimidines, or simpler natural bases, and hence is of great biochemical value. Monosubstituted ureas, thiourea, urethane, and biuret, however, yield sparingly soluble condensation products. 

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