Urea derivatives cyclic

Scheme 36. The urea derivative gave similar results to the thiourea compound. Acyclic imines (mainly E isomers) and Z cyclic imines could also be used for this process (Scheme 40,91% ee) [148,152,154].

N-( 1,1 -Dialkylprop-2-ynyl)ureas, bearing a bidentate ureic function, afforded oxazoline and cyclic ureas derivatives simultaneously, depending on whether the cyclization was initiated by the oxygen or the nitrogen atom (Eq. 46) [106]. The nature of the nitrogen substituent strongly influenced the product distribution. 

Preparation of cyclic urea derivatives by the intramolecular condensation of l,l,3,3-tetrakis(2-chloroethyl)urea [106]. 

Urea itself is the starting material for the preparation of various important linear and cyclic urea derivatives. For example, the reaction of formaldehyde with urea leads to 1,3-dimethylolurea. Heating this product converts it into a polymeric methyleneurea resin of wide industrial importance in adhesives and coatings. 

Initially, water can cause the hydrolysis of the anhydride or the isocyanate, Scheme 28 (reaction 1 and 2), although the isocyanate hydrolysis has been reported to occur much more rapidly [99]. The hydrolyzed isocyanate (car-bamic acid) may then react further with another isocyanate to yield a urea derivative, see Scheme 28 (reaction 3). Either hydrolysis product, carbamic acid or diacid, can then react with isocyanate to form a mixed carbamic carboxylic anhydride, see Scheme 28 (reactions 4 and 5, respectively). The mixed anhydride is believed to represent the major reaction intermediate in addition to the seven-mem bered cyclic intermediate, which upon heating lose C02 to form the desired imide. The formation of the urea derivative, Scheme 28 (reaction 3), does not constitute a molecular weight limiting side-reaction, since it too has been reported to react with anhydride to form imide [100], These reactions, as a whole, would explain the reported reactivity of isocyanates with diesters of tetracarboxylic acids and with mixtures of anhydride as well as tetracarboxylic acid and tetracarboxylic acid diesters [101, 102]. In these cases, tertiary amines are also utilized to catalyze the reaction. Based on these reports, the overall reaction schematic of diisocyanates with tetracarboxylic acid derivatives can thus be illustrated in an idealized fashion as shown in Scheme 29. 

Urea, 3-oxo-A4-1,2,4-thiadiazolin-5-yl-synthesis, 6, 592 Urea, thio-cyclic derivatives toxicity, 1, 138-139 toxicity, 1, 139 Urethane foam catalysts, 1, 405-406 Urethanes... 

Solov ev, V.P Vamek, A. Anti-HIV activity of HEPT, TIBO, and cyclic urea derivatives Structure-property studies, focused combinatorial library generation, and hits selection using substructural molecular fragments method. J. Chem. Inf. Comp. Sci. 2003,43 (5), 1703-1719. 

Keywords Carbon dioxide Polyethylene glycol C02 transformation Cyclic carbonates Dimethylcarbonate Oxazolidinones Organic carbamates Urea derivatives... 

As an abundant, nontoxic, non-flammable, easily available, and renewable carbon resource, C02 is very attractive as an environmentally friendly feedstock for making commodity chemicals, fuels, and materials [1-7]. In this respect, PEGs-functionalized catalysts have been developed for efficient transformation of C02 into value-added chemicals or fuels such as cyclic carbonates, dimethyl carbonate (DMC), oxazolidinones, organic carbamates and urea derivatives. 

If the latter reaction proceeds through a closed transition state (e.g., 5 in Scheme 7.2), good diastereocontrol can be expected in the case of trans- and cis-CrotylSiCl3 (2b/2c) [14, 15]. Here, the anh-diastereoisomer 3b should be obtained from trans-crotyl derivative 2b, whereas the syn-isomer 3c should result from the reaction of the cis-isomer 2c (Scheme 7.2). Furthermore, this mechanism creates an opportunity for transferring the chiral information if the Lewis base employed is chiral. Provided that the Lewis base dissociates from the silicon in the intermediate 6 at a sufficient rate, it can act as a catalyst (rather than as a stoichiometric reagent). Typical Lewis bases that promote the allylation reaction are the common dipolar aprotic solvents, such as dimethylformamide (DMF) [8,12], dimethyl sulfoxide (DMSO) [8, 9], and hexamethylphosphoramide (HMPA) [9, 16], in addition to other substances that possess a strongly Lewis basic oxygen, such as various formamides [17] (in a solution or on a solid support [7, 8, 18]), urea derivatives [19], and catecholates [10] (and their chiral modifications [5c], [20]). It should be noted that, upon coordination to a Lewis base, the silicon atom becomes more Lewis acidic (vide infra), which facilitates its coordination to the carbonyl in the cyclic transition state 5. 

Reaction of a primary cyclic enaminoester with aryl isocyanates yield urea derivatives, which can be cyclized to fused uracils10 (equation 6). 

At a pressure of two atmospheres uracil III is reduced nearly quantitatively in aqueous solution to hydrouracil IV by action of hydrogen gas in presence of colloidal platinum. For example, when six grams of this pyrimidine were agitated in the reductor at a temperature of 75-85° C. and at a pressure of two atmospheres the reduction was complete at the end of seven hours, and almost a theoretical amount of hydrogen had added to the pyrimidine. The reduced pyrimidine melted at 272° C. and corresponded in all its chemical and physical properties witli hydrouracil prepared by application of Hoffmann s reaction to sucdnimide.4 It did not respond to Wheeler and Johnson s test for uracil 5 We are now engaged in determining whether hydrouradl can be reduced still further by our catalytic method to the cyclic urea derivative of syn-trimethylenediamine V. 

Cyclic urea derivatives, (IV), prepared by Hutchinson (4) and amine salt derivatives, (V), prepared by Wells (5) were effective as v(i3 and/or v(i5 receptor integrin antagonists and used for inhibiting bone resorption disorders including osteoporosis and periodontal disease. 

Generation of 10 from the corresponding bis(iminophosphorane) using B0C2O in the presence of DMAP, resulted in the formation of the corresponding cyclic urea derivative. However, low yields of 10 are also obtained from bis(iminophhosphoranes) and isothiocyanates. 

A terminal cyclic urea derivative of valine is present at one terminus in lopinavir (43). Preparation of this heterocyclic moiety begins with conversion of valine (35) to its phenoxycarbonyl derivative by reaction with the corresponding acid chloride. Alkylation of the amide nitrogen with 3-chloropropylamine in the presence of base under very carefully controlled pH results in displacement of the phenoxide group to give the... 

Surprisingly, the symmetric cyclic sulfo-nyl-urea derivative analog (88) (Fig. 15.38, Ki = 3 nM) binds differently in the active site and adopts a flipped conformation (156). 

Debnath, A.K. (1998). Comparative Molecular Field Analysis (CoMFA) of a Series of Symmetrical Bis-Benzamide Cyclic Urea Derivatives as HIV-1 Protease Inhibitors. J.Chem.Inf.Com-put.ScL, 38,761-767. 

Carboxylic acid azides give rise to three different reactions under different conditions. Azide coupling (equation 9) was the earliest method in peptide synthesis and is still one of the most important in fragment condensation and preparation of cyclic peptides due to its almost complete lack of racemization. At elevated temperatures a frequent side reaction is the Curtius rearrangement. Trapping of the intermediate isocyanate with amines (equation 10) gives urea derivatives and with carboxylic acids rearranged amides are obtained (equation 11). ... 

Dihydroquinazottn-2-ones. Methyl o-(Al-triphenylphosphoranylimino)cinna-mate is converted to mixed carbodiimides on reaction with RN=C=0. TBAF promotes cyclization of the carbodimides to give 2-fluoro-3,4-dihydroquinazoline derivatives. Cyclic ureas are obtained on hydrolysis. 

The reaction of Me jCPCSiMe 3) j with phosgene occurs with the elimination of Me3SlCl and CO, and the formation via several detectable intermediates) of a cyclic phospha-urea derivative, (10.31), as illustrated in the following scheme [71] ... 

HIV-1 protease (HIV-1 PR) Non-peptide, C2-symmetric cyclic urea derivatives were designed de novo to fit the HlV-i PR active site. These novel, conformationally-constrained inhibitors feature a diol functionality that interacts with the catalytic aspartates while an urea oxygen mimics a structural water mediating substrate interactions with the enzyme flap. The required absolute configuration at four chiral centers was correctly predicted. Potent, bioavailable clinical candidates emerged from this work. i37 ... 

Dehnath, A.K (1998) Comparative molecular field analysis (CoMFA) of a series of symmetrical his-henzamide cyclic urea derivatives as HIV-1 protease inhibitors./. Chem. Inf. Comput. Sci., 38, 761-767. 

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