With cyclic ureas

Scheme 11.1 Cold catalyzed asymmetric hydroamination of alkenes with cyclic ureas [12].

Semicarbazide gives 3-aminoquinazolinedione (175).76,207 Reaction of IA with guanidine forms the diquinazolone 177207 and with cyclic ureas such as 176 tetracyclic quinazolones (178) are produced217 (Scheme 29). 

Zhang Z, Lee SD, Widenhoefer RA. Intermolecular hydroa-mination of ethylene and 1-alkenes with cyclic ureas catalyzed by achiral and chiral gold(I) complexes. J. Am. Chem. Soc. 2009 13(15) 5372-5373. 

Cyclic ureas can be obtained by reaction of simple urea with 1,2-diamino derivatives in DMF in the presence of ZnO and under microwave irradiation (Scheme 53). In this unusual condensation, two molecules of ammonia are eliminated. The reaction is very sensitive to the presence of ZnO. Without this catalyst, a yield of 20% is reported together with the formation of several by-products. The reaction was also carried out under reduced pressure... 

The benzyl phosphonate triesters 100 reacted with isocyanates under similar conditions to give the corresponding cyclic urea phosphonate diesters 101 (2). 

The cyclic disilazane 2012, which is readily accessible by treatment of 45 with NH3, reacts with the urea-H202 adduct to give, in 68% yield, the liquid cyclic analogue 2013 of BTSP 1249 2013 seems, to be more hindered and thus less reactive than BTSP 1949 [183] (Scheme 12.53). 

Diazidobiphenyl is transformed by diiron nonacarbonyl into a cyclic urea together with a small amount of the bridged dinuclear complex 142 the latter is a minor product but it can be converted oxidatively into benzocinnoline (Scheme 165).191... 

Warshel and coworkers have recently examined the LIE method and different versions of what they call the LRA (linear response approximation) method for the binding of a set of cyclic urea compounds to HIV protease.34 The key features of their LRA scheme is that both averages of Equation 2 are evaluated, thus requiring two extra simulations of the non-polar states (see above), that the ligand intramolecular electrostatic terms are included in the averages, and that the non-polar contribution is calculated with the PDLD method. Results of similar quality were reported with the different methods.34 However, it should be noted that the value Vi of the electrostatic coefficient was used in Ref. 34, which, as discussed above, has been shown... 

Symmetrical dialkyl and diaryl thioureas have been prepared in generally good yield (60-90%) from the reaction of the amine with thiophosgene, formed in situ from the catalysed reaction of carbon tetrachloride with sodium sulphide [5], Reaction with diamines yields cyclic ureas. 

Eaton and co-workers ° synthesized the cubane-based dinitrourea (42) via iV-nitration of the cyclic urea (41) with nitric acid-acetic anhydride. Cubane-based nitramide (43) is prepared from the IV-nitration of the corresponding bis-amide with acetic anhydride-nitric acid. Bis-nitramine (44) is prepared from the IV-nitration of the corresponding diamine with TFAA-nitric acid. ... 

It is of interest to note that a simple tetrahydropyrimidine, such as the 2-hydroxy derivative (XCIX), which actually is a cyclic urea, with the two protons probably on the nitrogen atoms, rather than the tautomer shown here. 

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. 

Lam et al. (1994) have also used this trick of both mimicking and displacing the water molecule. They designed a series of 7-membered ring cyclic ureas, including 68, which is a potent enzyme = 0.27 nM) and virus inhibitor, and also has significant oral bioavailability. This compound is currently under clinical investigation. Crystal structures of 10 of these cyclic urea complexes with protease have been determined, and show that, as the... 

The condensation of 1,4-diamines with a variety of carboxylic acid derivatives, e.g. imidate esters, orthoformic esters, /V-ethoxycarbonylthioamides (77JOC2530), nitriles and ethoxyacetylene, produces the cyclic amidine linkage —N = C(R)NH— (67AHC(8)2l, p. 40). Cyclic ureas, —NHC(0)NH—, have been similarly produced using carbonyl chloride, A, A -carbonyldi imidazole, carbon monoxide, thiocarbonyl chloride or carbon disulfide (67AHC(8)21, p. 38). 

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