Search results for "urea"
showing 10 items of 888 documents
ChemInform Abstract: Cooperative Assistance in Bifunctional Organocatalysis: Enantioselective Mannich Reactions with Aliphatic and Aromatic Imines.
2013
both of which contain a thiourea moiety (Scheme 1).The catalysts are capable of deprotonating suitable nucleo-philes, such as activated carbonyl compounds. This proton-transfer reaction generates an ion pair, which is composed ofthe protonated catalyst and the anionic nucleophile interact-ing through hydrogen bonds. At least one of the NH moietiesin the protonated catalyst is involved in activating theelectrophilic reaction partner.
New Sesquiterpene Lactones and Other Constituents fromCentaurea paui
1997
Aerial parts of Centaurea paui afforded, in addition to several known sesquiterpene lactones, the two new elemanolides 2–4, the new elemane derivative 5 as well as the five new heliangolides 14–18. Their structures were elucidated by spectroscopic methods, especially high-field NMR spectroscopy. The structure of the heliangolide 12 previously isolated from this plant, has been confirmed by X-ray diffraction.
Tetra-Urea Calix[4]arenes— From Dimeric Capsules to Novel Catenanes and Rotaxanes
2008
Wide Rim Urethanes Derived from Calix[4]arenes: Synthesis and Self-Assembly
2006
[reaction: see text] Calix[4]arenes 4, substituted at the wide rim by four N-tolyl-urethane groups, were synthesized, as well as derivatives 10a,b bearing two or three tolyl-urea groups beside of one or two urethane group(s). In contrast to tetra-tolyl urea 11, the urethane derivatives do not form hydrogen-bonded, dimeric capsules in CDCl3 or benzene-d6, but the dimerization can be induced for the triurea 10b by tetraethylammonium cations as guests. The quantitative formation of heterodimers is observed for all urethanes 4 and 10a,bin benzene-d6 in mixtures with a "tetra-loop" tetraurea 14, while "bisloop" tetraureas 13 require di- or triurea derivatives 10a,b for a clean heterodimerization.
H2-Antihistaminika, 6. Mitt. Synthese und Wirkung N-substituierter 4-[(2-Amino-ethylmercapto)-methyl]-imidazole
1980
Es wurden die N-substituierten 4-[(2-Amino-ethylmercapto)-methyl]-imidazole 2 und 3 dargestellt und auf histaminartige Wirkung untersucht. Die Thioharnstoff- und Cyanoguanidin-Derivate von 3b zeigten keine H2-antihistaminische Wirksamkeit. H2-Antihistaminics, VI: Synthesis and Activity of N-Substituted 4-[(2-Aminoethylmercapto)methyl]imidazoles The N-substituted 4-[(2-aminoethylmercapto)methyl]imidazoles 2 and 3 were prepared and tested for their histamine-like activity. The thiourea and cyanoguanidine derivatives of 3b showed no H2-antihistaminic activity.
ChemInform Abstract: Tetra-urea Calix[4]arenes - From Dimeric Capsules to Novel Catenanes and Rotaxanes
2009
ChemInform Abstract: Rotaxanes and Catenanes Derived from Tetra-Urea Calix[4]arenes
2011
Sesquiterpene lactones of two centaurea species from Sicily
1998
ChemInform Abstract: Organocatalytic Asymmetric Addition of Naphthols and Electron-Rich Phenols to Isatin-Derived Ketimines: Highly Enantioselective …
2015
A quinine-derived thiourea organocatalyst promoted the highly enantioselective addition of naphthols and activated phenols to ketimines derived from isatins. The reaction afforded chiral 3-amino-2-oxindoles with a quaternary stereocenter in high yields (up to 99 %) with excellent enantioselectivity (up to 99 % ee). To the best of our knowledge, this transformation is the first highly enantioselective addition of naphthols to ketimines.