Dialkyl urea

Scheme 6/1.97. Pd"-catalyzed 1,2-diamination of isoprene with N.N-dialkyl ureas.

Fig. 8.9. O-Sulfonylation of the asymmetric /V,A/-dialkyl urea A with tosyl chloride/ triethylamine and subsequent, deprotonation to the unsymmetrical N,N dialkylcarbodiimide D.

Thiazolidinedione (2) is readily alkylated at the 3-position when treated with alkyl chlorides for 5 minutes at 142°-145° in DMF with potassium carbonate (Scheme 2).101 Prolonged reaction at temperatures above 120° resulted in decreased yields of 82 and in formation of 1,3-dialkylated ureas via ring degradation.101 Treatment of the potassium salt of 2 (83) with primary alkyl halides102 has been demonstrated to be the most versatile alkylation procedure, by which a wide range of functionalized side chains have been appended to the 3-position.103-106 3-Methylthiazolidine-dione (82 R = Me) is conveniently prepared from 2 by treatment with... 

In the case of N,N -dialkyl ureas, phosgene is attacked by both oxygen and nitrogen atoms to give a mixture of chloroformamidinium chlorides (A) (0-acylation of the ureas) and allophanoyl chlorides (B) (N-acylation) as shown in scheme 155 (Ref. 211). 

The distribution of O-acylation and N-acylation can be slightly controlled by the reaction conditions, but structural features of the N,N -dialkyl ureas seem to be the dominant factors. 

The mechanism of the P-M oxidation consists of three distinct steps 1) activation of the DMSO by a protonated dialkyl carbodiimide 2) activation of the alcohol substrate and the formation of the key alkoxysulfonium ylide intermediate and 3) the intramolecular decomposition of the alkoxysulfonium ylide to afford the product ketone or aldehyde and the dialkyl urea by-product (established by isotopic labeling studies). The alkoxysulfonium ylide is a common intermediate in all other oxidations using activated DMSO. 

Fluorous scavengers do not necessarily need to form a covalent bond with the species they have to remove into the fluorous phase. For example, lightly fluorous N,N -dialkyl ureas can bind to perfluorocarboxyl ic acids by hydrogen... 

Scheme 3.26 Lightly fluorous N.N -dialkyl urea (Rp = QFn) has a relatively low partition coefficient of 30 70 in a C-Fp/CHjCIj biphasic system. After addition of perfluoroheptanoic acid, the partition coefficient of the resulting hydrogen bonded complex is 99 1, and the urea is completely removed from the organic into the fluorous phase [29].

Hydrocarbons Bile acids Sapogenins N-Aryl-N, N -dialkyl-urea herbicides [79] [81,82] [84] [86] rooi Cholestanone, a-cholestanol Triterpene derivatives CycltAexanol Sulfur-containing polysaccharides [80] [83] [85] [87]... 

Thiazolines are readily alkylated at the nitrogen atom when treated with alkyl chlorides, yielding A -alkyl-2-thiazolinium salts. Prolonged reaction at temperatures above 120°C resulted in decreased yield of alkylated product and in formation of 1,3-dialkylated ureas via ring degradation... 

The most important and most active compounds of the urea group are the N-aryl-NJN -dialkyl ureas. In these compounds the aryl group carries not more than two substituent groups, and none of these can be in the ort/jo-position. The monosubstitution (in meta- or para-position) and the disubstitution (in 3,4-positions) are most favourable. 

Diary] and triaryl or naphthyl carbamates exhibit low herbicidal activity. The substitution of the aryl radical for a heterocyclic radical gives heterocyclic alkyl and dialkyl ureas, of which many examples have been prepared in recent years. The herbicidal activity of urea derivatives containing a heterocyclic radical, such as benzthiazole, thiazole, thiadiazole, oxadiazole and pyridine, is favourable if one or two methyl groups are substituted at the N -nitrogen. The carrier of total or selective action in these derivatives is presumably the heterocyclic part of the molecule. More recently several new groups of compounds have become known, mainly in the patent literature, for which the structure-activity on relationships are still to be elucidated. 

They have a lower biological activity and persistence than the aryl-dialkyl ureas discussed above, but their selectivity is greater. These derivatives can safely be used as selective weed killers in sensitive crops. 

Secondary nitramines are prepared by the nitrolysis of secondary amides or of N,N-dialkyl ureas... 

X- = NCO From Amberlyst A-26 (Cl ) by treatment with aq. KOCN Symmetrical MN -dialkyl ureas from primary and secondary as well as from benzylic and allylic halides if the reaction was performed with wet resin in apolar solvents, N-Substituted ethyl urethanes were obtained from alkyl and benzyl halides if the reaction was carried out in EtOH. 

Mack et al. carried out A -alkylation reaction in ball mill (8000M SpexCertiprep Mixer Mill, stainless steel) [46], Reaction of 4-bromobenzyl bromide 257 with urea and sodium hydroxide yielding di-(4-bromobenzyl) urea 258 proved that chemical reactions under high-speed ball-milling conditions could be manipulated in order to increase the nucleophilicity of an otherwise weakly nucleophilic substance (Scheme 3.68). Here the hydroxide deprotonates the urea, increasing the nucleophilicity of the nitrogen. Withont NaOH, there was a negligible conversion to a dialkyl urea product. 

Because of the tertiary nitrogen, these reactant resins cannot form chloroamines and therefore cannot evolve any hydrogen chloride. In addition, 4,5-dihydroxy-1,3-dimethylol ethylene urea is tetrafunctional, since the CHOH groups in the 4 and 5 positions also possess methylol characteristics. Cotton treated with triazone is more stable to acids and alkalis than DMEU products, but it has to be rinsed well because of its fishy odor. In addition, it tends to become yellow at high temperatures. AT,N -Di-methylol-N,iV -dialkyl urea, on the other hand, cannot be employed as a reactant resin since its equilibrium tends considerably toward the formaldehyde side ... 

In symmetrical dialkyl ureas the 1575 cm" band vanishes whereas those at 1656 and 1610 cm" remain. In contrast, in unsymmetrical dialkyl ureas, it is the 1656 cm" band which vanishes whilst the others remain. Other symmetrical dialkyl ureas have been studied by Mido [165] with similar results. He quotes pqo in the 1640—1625 cm" range with little deuterium sensitivity, and the D-sensitive amide II band at 1580 cm". Kutepov [166] et al. have studied symmetrical diaryl ureas where the carbonyl band appears close to 1640 cm" Gompper et al. [115] have discussed the characteristic frequencies of the NH—CO—N— grouping in cyclic systems. 

Tetrahydropyran-2-yl isocyanate, preparable from 2-chlorotetrahydropyran and AgCNO, reacts with amines to form monoalkyl ureas or unsymmetrical dialkyl ureas, and with alcohols to form alkyl carbamates. ... 

The spectra of ureas show many similarities to the spectra of amides. The C=0 and NH2 bands are similar to those of amides with some small shifts. The N,N -dialkyl ureas have two NH bonds and this complicates the CNH region, normally around 1550 cm Approximate wavenumbers for substituted ureas in the solid state are listed in Table 9.12 where R is an alkane group. 

CO2 can be one of the substrates for the synthesis of dialkyl urea and cyclic urethane compounds that have found extensive applications as dyes, antioxidants, and intermediates for the preparation of pharmaceuticals and agricultural chemicals. In this section, some examples where ILs could successfully be used for these reactions wiU be described. 

Scheme 32. Synthesis of dialkyl urea from amine and CO2.

Lately, Jiang et al. [107] used [BMlm]OH for the dialkyl ureas under conditions similar to those employed by Deng et al. This catalyst also gave good yields of diatkyl ureas, although slightly longer reaction time was required. Unfortunately, no urea was obtained from aniline, which could afford N,N -diphenyl urea with CO2 by [BMIm]OH/CsOH. No ureas were produced from dibutyl amine and from tiibutyl amine. Scheme 33 illustrates a reaction mechanism proposed by the authors. 

Scheme 33. A proposed mechanism for the synthesis of dialkyl urea from amine and CO2 catalyzed by [BMImjOH [107].

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