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(Thio)urea organocatalysis describes the utilization of properly designed derivatives of urea and thiourea to accelerate and stereochemically alter organic transformations through predominantly double hydrogen-bonding interactions with the respective substrate(s) (non-covalent organocatalysis). The scope of these small-molecule H-bond donors termed (thio)urea organocatalysts covers both non-stereoselective and stereoselective applications in organic synthesis (asymmetric organocatalysis). In nature non-covalent interactions such as hydrogen bonding ("partial protonation") play a crucial role in enzyme catalysis that is characterized by selective substrate recognition (molecular recognition), substrate activation, and enormous acceleration and stereocontrol of organic transformations. Based on the pioneering examinations by Kelly, Etter, Jorgensen, Hine, Curran, Göbel, and De Mendoza (see review articles cited below) on hydrogen bonding interactions of small, metal-free compounds with electron-rich binding sites Schreiner and co-workers performed series of theoretical and experimental systematic investigations towards the hydrogen-bonding ability of various thiourea derivatives.〔Alexander Wittkopp, Peter R. Schreiner, ''"Diels-Alder Reactions in Water and in Hydrogen-Bonding Environments"'', book chapter in "The Chemistry of Dienes and Polyenes" Zvi Rappoport (Ed.), Volume 2, John Wiley & Sons Inc.; Chichester, 2000, 1029-1088. ISBN 0-471-72054-2. Alexander Wittkopp, ''"Organocatalysis of Diels-Alder Reactions by Neutral Hydrogen Bond Donors in Organic and Aqueous Solvents"'', dissertation written in German, Universität Göttingen, 2001. english abstract/download: () Peter R. Schreiner, review: ''"Metal-free organocatalysis through explicit hydrogen bonding interactions"'', ''Chem. Soc. Rev.'' 2003, ''32'', 289-296. abstract/download:() Christian M. Kleiner, Peter R. Schreiner, ''"Hydrophobic amplification of noncovalent organocatalysis"'', ''Chem. Commun.'' 2006, 4315-4017.abstract/download:() Yoshiji Takemoto, review: ''"Recognition and activation by ureas and thioureas: stereoselective reactions using ureas and thioureas as hydrogen-bonding donors"'', ''Org. Biomol. Chem.'' 2005, ''3'', 4299-4306. abstract/download: () 〕 These purely organic compounds were found to reveal significant rate enhancements of simple Diels-Alder reaction, act like weak Lewis acid catalysts, but operate through explicit double hydrogen bonding instead of covalent (strong) binding known from traditional metal-ion mediated catalysis and Brønsted acid catalysis. ==Overview== Schreiner and co-workers identified and introduced electron-poor thiourea derivatives as hydrogen-bonding organocatalysts. ''N,N-bis]"), sustainable catalysts To date various organic transformations are organocatalyzed through double hydrogen-bonding ''N,N-bis()phenyl thiourea at low catalyst loadings and in good to excellent product yields. This electron-poor thiourea derivative enjoys the status of being a privileged catalyst and represents the benchmark for the design of a broad variety of explicit double hydrogen-bonding (thio)urea organocatalysts - achiral, and chiral as well as monofunctional and bifunctional representatives: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Thiourea organocatalysis」の詳細全文を読む スポンサード リンク
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