Ureas tetrasubstituted

Tertiary amines react with phosgene to give symmetrical tetrasubstituted ureas (Eq. 28). (See Table II.) This reaction probably involves the intermediate... 

Reaction of Tertiary Amines with Phosgene to Give Symmetrical Tetrasubstituted Ureas... 

UV-visible spectroscopic data for these systems also display a number of remarkable features. Thus, in the case of bulky thioamides and tetrasubstituted ureas, there are indications of the existence of two different 1 1 complexes. Their possible structures are presently being studied by means of high level ab initio calculations540. 

The imidazole derivative, prochloraz, has a peculiar feature compared to the azole derivatives. The nitrogen atom in the 1-position of the imidazole is bonded to a carbamoyl group and not to alkyl. This compound, which is regarded as a tetrasubstituted urea, has a very broad spectrum and can be used in cereals both as a seed dressing and a foliar fungicide (9). 

Other classes of aliphatic, nitrogen compounds examined as sugar solvents include nitriles, urethans, ureas, and amides. Of these, the amides are the most significant commercially, but a less-expensive synthesis of some of the tetrasubstituted ureas could furnish solvents... 

The utility of carbonylation of lithium amides for the synthesis of complex molecules has been also demonstrated. V.V.V V -Tetrasubstituted ureas 5 were obtained in good yields by reaction of lithium alkyl amides in THF solution with carbon monoxide under mild conditions (0°C, 1013 mbar), followed by treatment with oxygen prior to work-up... 

The reaction of phosgene with substituted ureas is well known. Phosgene reacts with tetrasubstituted ureas as a chlorinating agent to afford chloroformamidinium chlorides in high yields. This topic will be discussed in volume 2. 

As was found for the primary amines, the final product of the reaction depends largely upon the reaction conditions, not least because R NCOCl (R = Me, Et or Ph) is a very reactive compound, and can combine with an excess of the amine to form the tetrasubstituted urea [1392a, 1392b] ... 

The reaction proceeds via the formation of an isolable tetrasubstituted urea derivative, the carbonyl group of which reacts with phosgene to give an intermediate chloroformyl group, which then undergoes decarboxylation. Other derivatives (R = R = Et, Pr, Me CH, or Me(CH2)3 R = Me, R = Ph) were found to behave in a similar way [433]. 

Other compounds, such as quaternary ammonium halides or tetrasubstituted ureas, are reported to catalyse this reaction [1559aa]. 

Recently, however, tetrasubstituted urea compounds, for example N-acyl-N-aryl-N, N -dialkylureas, have been discovered, which also exhibit good herbicidal activity, though it is assumed that these compounds exert their herbicidal action after the splitting off of the acyl group, that is, in the trisubstituted form, containing free imino hydrogen. 

If the imidoyl halides are generated from N,N -disubstituted carboxylic acid amides, or from tetrasubstituted ureas, only iminium salts are formed. 

However, the reaction of tri- and tetrasubstituted ureas with carbonyl chloride affords high yields of the chloroformamidine hydrochlorides ( ). 

The commercially available and easily handled crystalline solid W,N -carbonyl-diimidazole (CDI) is utilized as a starting reagent for the general synthesis of unsymmetrical tetrasubstituted ureas. The intermediate carbamoyl imidazole 1017 is first obtained by reaction of CDI with a secondary amine. Compound 1017 is then converted into the more reactive and resonance-stabilized imidazolinium salt 1018 by N-alkylation of the imidazole moiety. Addition of a different secondary amine to 1018 furnishes N,N,N, N -unsymmetrical tetrasubstituted ureas 1019 in high yield (72-99%). 

Although numerous methods are available for the preparation of symmetrical and unsymmetrical di- or trisubstituted ureas in good to excellent yields, the only hitherto reported synthesis of unsymmetrical tetrasubstituted ureas involves reaction of a carbamoyl chloride (prepared from a secondary amine and phosgene) with a secondary amine [754]. Moreover, this method, as used more recently [755, 756], suffers from several drawbacks. An excess of amine and/or the use of an acid scavenger (such as pyridine or triethylamine) is required, and the carbamoyl chloride intermediate can be both unstable and difficult to isolate when needed. Moreover, the production of hydrochloric acid prevents the application of this method when acid-sensitive functionalities are present. N,N -Carbonyldibenzotriazole can be utilized to synthesize N,N,N, N -unsymmetrical tetrasubstituted ureas 1023 by a... 

N,N,N, N -Tetrasubstituted ureas 1049 have been obtained in variable yields (45-69%) by reaction of lithium aliphatic amides 1047 in THF solution with carbon monoxide under mild conditions (atmospheric pressure, 0 °C) followed by in situ oxidation with oxygen of the intermediate 1048 prior to work-up. The advantages of this method are the short reaction time and the use of molecular oxygen as oxidant [764]. 

Cyclic ureas 1068 were readily prepared from N-methylethylenediamine or hy-droxylated ethylenediamine in the presence of PhsSbO as a catalyst [777], but it was found that ethylenediamine, N-phenylethylenediamine, and N,N -dimethyl-ethylenediamine would not react with CO2. The modified catalyst Ph3SbO/P4Sio is highly active in the carbonylation of these diamines, and the corresponding 2-imidazolidinones were obtained at 80-150 °C (Table 4.34). It is interesting to note that tri- and tetrasubstituted ureas were readily obtained without thionation, even at 150 °C. 

N-Alkylation of ureas represents a further useful method for the selective synthesis of N,N,N, N -tetrasubstituted ureas, including cyclic ones. Thus, N,N -divinylpro-pyleneurea 1097 is prepared in 89% yield by the addition of vinyl propionate 1096 over a period of 15 min to a mixture of propyleneurea and dimethylaminopyridine (DMAP) at 95 °C and refluxing for 5.5 h [790],... 

It is now possible to write the polymerization of urea with formaldehyde as follows. The forward reactions can be easily written in terms of A to D (the formation of tetrasubstituted urea does not oeeur) as follows ... 

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