Monomeric Cinchona Alkaloid-Based Catalysts for Highly Enantioselective Bromolactonisation of Alkynes
作者:Michael Wilking、Constantin G. Daniliuc、Ulrich Hennecke
DOI:10.1002/chem.201604003
日期:2016.12.19
The cinchona alkaloid dimer (DHQD)2PHAL has been shown to be a broadly applicable catalyst for asymmetric halogenations. However, this catalyst does not have to be dimeric and a class of monomeric quinidine and quinine‐derived catalysts was prepared, often showing superior selectivity in bromolactonisations of terminal alkynoic acids. Mechanistic investigations show that these organocatalysts act as
Catalytic Enantioselective Halolactonization of Enynes and Alkenes
作者:Wei Zhang、Na Liu、Casi M. Schienebeck、Kyle Decloux、Suqing Zheng、Jenny B. Werness、Weiping Tang
DOI:10.1002/chem.201103809
日期:2012.6.4
developed for the enantioselectivehalolactonization of (Z)‐1,3‐enynes and 1,1‐disubstituted alkenes. In the case of 1,3‐enynes, the carboxylate nucleophile and halogen electrophile were added to the conjugated π‐system from the same face. Up to 99 % ee was achieved for the 1,4‐syn‐bromolactonization of conjugated (Z)‐1,3‐enynes. Based on the results from the enynehalolactonization, a second generation
Dissecting the Stereocontrol Elements of a Catalytic Asymmetric Chlorolactonization: <i>Syn</i> Addition Obviates Bridging Chloronium
作者:Roozbeh Yousefi、Kumar Dilip Ashtekar、Daniel C. Whitehead、James E. Jackson、Babak Borhan
DOI:10.1021/ja4072145
日期:2013.10.2
absolute and relative stereochemistry of addition in enantioselective chlorolactonizations of 4-phenyl-4-pentenoic acid and its related t-butyl ester, catalyzed by (DHQD)2PHAL. Predominant syn addition of the chlorenium and the nucleophile across the olefin is observed. As shown by isotopic labeling, NMR spectroscopy, and derivative studies, the two new stereocenters formed by addition across the double
Mechanistic Insights into the Origin of Stereoselectivity in an Asymmetric Chlorolactonization Catalyzed by (DHQD)<sub>2</sub>PHAL
作者:Roozbeh Yousefi、Aritra Sarkar、Kumar Dilip Ashtekar、Daniel C. Whitehead、Tayeb Kakeshpour、Daniel Holmes、Paul Reed、James E. Jackson、Babak Borhan
DOI:10.1021/jacs.0c01830
日期:2020.4.15
Electrophilic halofunctionalization reactions have undergone a resurgence sparked by recent discoveries in the field of catalytic asymmet-ric halocyclizations. To build mechanistic understanding of these asymmetric transformations, a toolbox of analytical methods has been deployed, addressing the roles of catalyst, electrophile (halenium donor), and nucleophile in determining rates and stereopreferences