Enantioselective Organocatalytic Intramolecular Diels−Alder Reactions. The Asymmetric Synthesis of Solanapyrone D
作者:Rebecca M. Wilson、Wendy S. Jen、David W. C. MacMillan
DOI:10.1021/ja054008q
日期:2005.8.24
The first direct enantioselective organocatalytic intramolecularDiels-Alderreaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction
High-Resolution Single-Turnover Mapping Reveals Intraparticle Diffusion Limitation in Ti-MCM-41-Catalyzed Epoxidation
作者:Gert De Cremer、Maarten B. J. Roeffaers、Evelyne Bartholomeeusen、Kaifeng Lin、Peter Dedecker、Paolo P. Pescarmona、Pierre A. Jacobs、Dirk E. De Vos、Johan Hofkens、Bert F. Sels
DOI:10.1002/anie.200905039
日期:2010.1.25
influence on catalysis are directly observed for individual catalytic particles by single‐turnover mapping using high‐resolution fluorescence microscopy. The Thiele modulus could be measured with just one experiment, proving the existence of diffusionallimitations for the Ti‐MCM‐41 catalyzed epoxidation of a fluorescent reporter molecule (see picture; TBHP=tert‐butylhydroperoxide).
Kinetics of proton transfer from phosphonium ions to electrogenerated bases: polar, steric and structural influences on kinetic acidity and basicity
作者:Ana-Paula Bettencourt、Ana Maria Freitas、M. Irene Montenegro、Merete Folmer Nielsen、James H. P. Utley
DOI:10.1039/a708086g
日期:——
linear sweep voltammetry (LSV) have been used to measure rates of protontransfer in DMSO solution between different types of electrogeneratedbase (EGB) and a series of phosphonium ions of relevance to ylide formation for synthetic reactions. Although the electrochemical methods are convenient for the measurement of rates of protontransfer in these systems a major conclusion of the study is that considerable
导数循环伏安法(DCV)和线性扫描伏安法(LSV)已用于测量DMSO溶液中质子在不同类型的电生成碱(EGB)与一系列与叶立德形成有关的合成反应之间的transfer离子转移速率。尽管电化学方法可方便地测量这些系统中的质子转移速率,但这项研究的主要结论是,在应用这些方法并从结果中得出一般结论时必须格外小心。尤其是将动酸度与热力学p K进行比较DMSO中的值表明,一系列Br离子不满足单个布朗斯台德关系。动酸度受到以下因素的严重影响:EGB是碳还是氮碱;一些the离子的烯醇化倾向;和空间因素。在酸性亚甲基上的其他电子需求量度(13 C和1 H化学位移,还原电位)与p K(DMSO)值一致。动力学结果证实,对于不可烯醇化的salts盐,Ph 3 P +基团比Bu 3 P +更具活化性。
Establishment of a general one-pot cascade reaction protocol would dramatically reduce the effort of multistep organic synthesis. We demonstrate that the unique structure of M12L24 self-assembled complexes gives them the potential to serve as catalyst carriers for enabling continuous chemical transformations. A stereoselective cascade reaction (allylic oxidation followed by Diels-Alder cyclization) with two
C−H Activation in Phosphonium Salts Promoted by Platinum(II) Complexes
作者:Larry R. Falvello、Susana Fernández、Carmen Larraz、Rosa Llusar、Rafael Navarro、Esteban P. Urriolabeitia
DOI:10.1021/om001034i
日期:2001.4.1
bis-phosphonium salts [R2PhPCH2]2C(O)}Cl2 (R2 = Ph2, PhEt, Et2) (1:1 molar ratio) in refluxing 2-methoxyethanol affords the C,C-orthometalated complexes [PtCl2(C6H4-2-PR2C(H)C(O)CH2PPhR2)] (R2 = Ph2 1a, PhEt 1b, Et2 1c). The reaction of PtCl2 with the bis-phosphonium salt [Ph3PCH2]2C(O)}Cl2 (1:1 molar ratio) gives [Ph3PCH2]2C(O)}[PtCl4], 2, while treatment of PtCl2 with the perchlorate salts [R2PhPCH2]2C(O)}(ClO4)2