Allenic ureas

The Widenhoefer group extended the method to the synthesis of enantiomerically enriched 2-vinylpyrrolidines from monosubstituted or trisubstituted y-aminoallenes, as well as allenic ureas, in the presence of chiral gold catalysts derived from [Au2 (S)-3,5-r-Bu-4-MeO-MeOBIPHEP Cl2] and a silver salt (Scheme... 

Hydroaminomethylahon of alkenes [path (c)j wiU not be considered [12]. This review deals exclusively with the hydroaminahon reaction [path (d)], i.e. the direct addition of the N-H bond of NH3 or amines across unsaturated carbon-carbon bonds. It is devoted to the state of the art for the catalytic hydroamination of alkenes and styrenes but also of alkynes, 1,3-dienes and allenes, with no mention of activated substrates (such as Michael acceptors) for which the hydroamination occurs without catalysts. Similarly, the reachon of the N-H bond of amine derivatives such as carboxamides, tosylamides, ureas, etc. will not be considered. 

Enol ether additives were used to probe the protonation of 3-cyclopen-tenylidene (127). Treatment of A-nitroso-A-(2-vinylcyclopropyl)urea (124) with sodium methoxide generates 2-vinylcyclopropylidene (126) by way of the labile diazo compound 125 (Scheme 25). For simplicity, products derived directly from 126 (allene, ether, cycloadduct) are not shown in Scheme 25. The Skat-tebpl rearrangement of 126 generates 127 whose protonation leads to the 3-cyclopentenyl cation (128). In the presence of methanol, cyclopentadiene (130) and 3-methoxycyclopentene (132) were obtained.53 With an equimolar mixture of methyl vinyl ether and methanol, cycloaddition of 127 (—> 131)... 

Inner root sheath proteins have been obtained from tissue dissected from the roots of rat vibrissae and porcupine quills and then extracted with 8 M urea containing iodoacetate and pH 8 buffer. The inner root sheath proteins (Table VI) and those isolated from the medulla of hair or porcupine quill are unusual in containing citrulline in protein combination (Rogers, 1958, 1962 Allen et al, 1964). 

Braun, D. Ritzert, H.-J. (1989) Urea-formaldehyde and melamine-formaldehyde polymers, in Allen, G. (Ed.) Comprehensive Polymer Science, Oxford Pergamon. 

Abstract Recent density functional theory computations of cobalt-catalyzed hydroformylation of propene, A -vinyl acetamide, 1,3-butadiene, acetylene, propyne, and allene and the urea formation from methyl amine as well as Pauson-Khand reaction have been reviewed. The detailed catalytic mechanism and regioselectivity have been discussed and compared with the available experimental data. It shows that modem computational chemistry provides not only qualitative but also quantitative aspects of catalytic reactions. 

Watson, R.J., Allen, D.R., Birch, H.L., Chapman, G.A., Galvin, F.C., Jophng, I-A., Knight, R.L., Meier, D. et al. (2008) Development of CXCR3 antagonists. Part 3 Tropenyl and homotropenyl-piperidine urea derivatives. Bioorganic Medicinal Chemistry Letters, 18, 147-151. 

Blouin, G. M., and A. W. Allen. 1985. A Study of Anticaking Treatments for Urea, TVA Circular Z-190, Presented at the 190th National Meeting of the American Chemical Society, September 9-12, Chicago, IL, U.S.A. 

In previons work (Allen et al., 1963 Tangpakdee et al., 1997), NR coagulated from fresh NR latex, just after tapping from Hevea brasiliensis, was found to be soluble in tolnene, cyclohexane, and tetrahydrofuran. In contrast, the mbber from latex preserved in the presence of ammonia contained about 30-70% gel fraction, which was insolnble in the solvents. The formation of the insoluble fraction would be concerned with the interactions of mbber and proteins, because the gel fractions are reported to be soluble in the solvents after the enzymatic deproteinization (Eng et al., 1994 Tangpakdee et al., 1997). If the interactions are physical but not chemical, it is possible to remove the proteins from the mbber after denaturation of the proteins with urea. Here, the removal of the proteins from fresh NR latex and preserved high-ammonia latex was investigated with mea in the presence of surfactant. 

In the hydroamination of unsaturated carbon-carbon bonds, gold catalysts play an important role. Intermolecular hydroamination of alkenes [177], 1,3-dienes [204], terminal and internal alkynes [205], and allenes [206] are known to proceed smoothly in the presence of PhsP AufI) or AuCls catalyst. In addition, amino olefins also efficiently undergo intramolecular hydroamination using similar gold catalysts. He and coworkers have developed the catalytic cycloaddition of tosylated amino olefins [207], A representative example is shown in Scheme 18.35. When N-tosylated y-amino olefin (97) is exposed to a mixture of PhsP AuCl and AgOTf (5 mol% each) in toluene at 85 °C, pyrrolidine (98) is obtained in 96% yield. The gold(I)-catalyzed intramolecular hydroamination is applicable to N-alkenyl carbamates [208], N-alkenyl carboxamides [209], and N-alkenyl ureas [210], The use of microwave irradiation results in completing the hydroamination in a much shorter time than that required under thermal reaction conditions [211], The... 

Catalytic, enantioselective halolactonization of (Z)-l,3-enynes (39) and 1,1-disubstituted alkenes with NBS has been reported to occur in the presence of chiral urea derivatives, such as (41), to produce allene derivatives (40) in <91% ee ... 

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