Enantioselective N‐Heterocyclic Carbene Catalysis by the Umpolung of α,β‐Unsaturated Ketones
作者:Yuji Nakano、David W. Lupton
DOI:10.1002/anie.201510106
日期:2016.2.24
N‐Heterocycliccarbene‐catalyzed formation of β‐anionic intermediates from enones has been employed in the enantioselective synthesis of 2‐aryl propionates. The reaction was achievable using a homochiral 4‐MeOC6H4 morpholinone catalyst allowing the first example of enantioselective catalysis by umpolung of α,β‐unsaturated ketones. The reaction is high yielding, and shows robustness with reasonable
N-杂环卡宾催化由烯酮形成的β-阴离子中间体已用于2-芳基丙酸酯的对映选择性合成。该反应可以通过使用手性4-MeOC 6 H 4吗啉酮催化剂来实现,这是通过α,β-不饱和酮的负载进行对映选择性催化的第一个例子。该反应收率高,并且具有合理的一般性的稳健性。提出了一种机制,其中使用六氟异丙醇或形成的萘酚产物实现对映体确定质子化。
Synthesis of Chiral Heterocyclic <i>N</i>
-Haloamides and -imides and Their Applications as Halogenating Agents and Mechanistic Probes
作者:Ulrich Hennecke、Christian H. Müller、Constantin G. Daniliuc
DOI:10.1002/ejoc.201601159
日期:2017.1.18
reports of chiral derivatives of the most common of these reagents such as N-halosuccinimides. Herein, we report the synthesis of new chiral N-halogenated amides and imide derivatives, which are easily accessible from inexpensive starting materials of the chiral pool. These new chiral halogenating agents were then applied as stoichiometric reagents in haloetherification reactions and as mechanistic probes
Chiraltriazolium salts bearing a pyridine ring were developed as N-heterocyclic carbene precursors. In the presence of the chiraltriazoliumsalt and a base, the catalytic asymmetricbenzoin condensation proceeded to afford the product in high level of chemical yield and enantioselectivity. A wide range of aromatic aldehydes were applicable to this reaction.
water-assisted hydrogen atom transfer mechanism. This finding led to a considerable enhancement in the experimental reaction rate while maintaining excellent enantioselectivity by adding catalytic amounts of water. Finally, computations and racemization experiments uncovered an uncommon Curtin–Hammett-controlled enantioselectivity in the presence of secondary-sphere modifiers.
Synthesis of enantiopure triazolium salts from pyroglutamic acid and their evaluation in the benzoin condensation
作者:Dieter Enders、Jianwei Han
DOI:10.1016/j.tetasy.2008.05.017
日期:2008.6
A family of enantiopure 1,2,4-triazolium salts were prepared starting from the inexpensive (S)-pyroglutamic acid. After treatment with base, the corresponding N-heterocyclic carbenes were tested as organo-catalysts in the asymmetric benzoin condensation and gave good yields and up to 95% ee. (C) 2008 Elsevier Ltd. All rights reserved.