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An organocatalytic enantioconvergent synthesis of chiral tetrasubstituted allenes is disclosed. With suitable chiral phosphoric acid catalysts, a range of racemic indole‐substituted propargylic alcohols reacted with nucleophiles to provide efficient access to a series of enantioenriched allenes with high enantioselectivities. Control experiments suggested a mechanism involving remotely controlled asymmetric 1,8‐addition of the in situ generated indole imine methide via a bifunctional transition state. 相似文献
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Enantioselective Synthesis of Quaternary Carbon Stereocenters: Addition of 3‐Substituted Oxindoles to Vinyl Sulfone Catalyzed by Pentanidiums 下载免费PDF全文
Dr. Lili Zong Shubo Du Kek Foo Chin Dr. Chao Wang Prof. Dr. Choon‐Hong Tan 《Angewandte Chemie (International ed. in English)》2015,54(32):9390-9393
A pentanidium‐catalyzed highly enantioselective conjugate addition of 3‐alkyloxindoles to phenyl vinyl sulfone has been demonstrated. This approach allows the construction of 3,3‐dialkyl‐substituted oxindole frameworks with high yield and excellent enantioselectivity (up to 99 %) under simple phase‐transfer conditions. A variety of oxindoles bearing all‐carbon quaternary stereogenic centers were obtained in the presence of 0.25 mol % pentanidium. Meanwhile, practicality was illustrated by a gram‐scale asymmetric synthesis of two 3,3‐dialkyl‐substituted oxindoles. The resulting adduct can be smoothly transformed to the natural product analogue in a short synthetic route. 相似文献
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Andrea‐Nekane R. Alba Xavier Companyó Guillem Valero Albert Moyano Prof. Dr. Ramon Rios Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5354-5361
A new, easy, and highly enantioselective method for the synthesis of quaternary α‐alkyl‐α‐amino acids based on organocatalysis is reported. The addition of oxazolones to 1,1‐bis(phenylsulfonyl)ethylene is efficiently catalyzed by simple chiral bases or thioureas. The reaction affords α,α‐disubstituted α‐amino acid derivatives with complete C4 regioselectivity and with excellent yields and enantioselectivities. This methodology is complementary to previously reported enantioselective approaches to quaternary α‐amino acids and allows the synthesis of α‐phenyl‐α‐alkyl‐α‐amino acids and α‐tert‐butyl‐α‐alkyl‐α‐amino acids. It has distinct advantages in terms of operational simplicity, enviromentally friendly conditions, and suitability for large‐scale reactions. 相似文献
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Organocatalytic Asymmetric 1,6‐Addition/1,4‐Addition Sequence to 2,4‐Dienals for the Synthesis of Chiral Chromans 下载免费PDF全文
Pernille H. Poulsen Karla Santos Feu Bruno Matos Paz Prof. Dr. Frank Jensen Prof. Dr. Karl Anker Jørgensen 《Angewandte Chemie (International ed. in English)》2015,54(28):8203-8207
A novel asymmetric organocatalytic 1,6‐addition/1,4‐addition sequence to 2,4‐dienals is described. Based on a 1,6‐Friedel–Crafts/1,4‐oxa‐Michael cascade, the organocatalyst directs the reaction of hydroxyarenes with a vinylogous iminium‐ion intermediate to give only one out of four possible regioisomers, thus providing optically active chromans in high yields and 94–99 % ee. Furthermore, several transformations are presented, including the formation of an optically active macrocyclic lactam. Finally, the mechanism for the novel reaction is discussed based on computational studies. 相似文献
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Jian Lv Dr. Jiaming Zhang Dr. Zhu Lin Dr. Yongmei Wang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(4):972-979
A general enantioselective synthesis of functionalized nitrocyclopropanes by organocatalytic conjugate addition of a variety of bromonitroalkanes to α,β‐unsaturated enone systems is presented. The process, efficiently catalyzed by the salts of 9‐amino‐9‐deoxyepiquinine 1 d serves as a powerful approach to the preparation of synthetically and biologically important cyclopropanes with high levels of enantio‐ and diastereoselectivities. Since only 0.6 equivalents of bromonitromethane are used as a reagent, (S)‐ 2 e is obtained enantiomerically pure by employing chiral 1 d as a highly efficient catalyst for its kinetic resolution (97 % ee at 51 % conversion, selectivity s=120). 相似文献
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A highly enantioselective three‐component hydroacyloxylation/1,4‐conjugate addition of ortho‐hydroxybenzyl alcohols, ynamides and carboxylic acids was developed under mild reaction conditions in the presence of a chiral N,N′‐dioxide/Sc(OTf)3 complex, which went through in situ generated ortho‐quinone methides with α‐acyloxyenamides, delivering a range of corresponding chiral α‐acyloxyenamides derivatives containing gem(1,1)‐diaryl skeletons in moderate to good yields with excellent ee values. The scale‐up experiment and further derivation showed the practicality of this catalytic system. In addition, a possible catalytic cycle and transition state model was proposed to elucidate the origin of the stereoselectivity based on X‐ray crystal structure of the α‐acyloxyenamide intermediate and product. 相似文献
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Enantioselective Organocatalytic Construction of Spiroindane Derivatives by Intramolecular Friedel–Crafts‐Type 1,4‐Addition 下载免费PDF全文
Dr. Keisuke Yoshida Yukihiro Itatsu Yuta Fujino Hiroki Inoue Prof. Dr. Ken‐ichi Takao 《Angewandte Chemie (International ed. in English)》2016,55(23):6734-6738
The highly enantioselective organocatalytic construction of spiroindanes containing an all‐carbon quaternary stereocenter by intramolecular Friedel–Crafts‐type 1,4‐addition is described. The reaction was catalyzed by a cinchonidine‐based primary amine and accelerated by water and p‐bromophenol. A variety of spiro compounds containing quaternary stereocenters were obtained with excellent enantioselectivity (up to 95 % ee). The reaction was applied to the asymmetric formal synthesis of the spirocyclic natural products (?)‐cannabispirenones A and B. 相似文献
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An Organocatalytic Mannich/Denitration Reaction for the Asymmetric Synthesis of 3‐Ethylacetate‐Substitued 3‐Amino‐2‐Oxindoles: Formal Synthesis of AG‐041R 下载免费PDF全文
Kun Zhao Tao Shu Jiaqi Jia Prof. Dr. Gerhard Raabe Prof. Dr. Dieter Enders 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):3933-3936
The highly enantioselective organocatalytic addition of ethyl nitroacetate to isatin‐derived N‐Boc ketimines (Boc=tert‐butoxycarbonyl), followed by the removal of the nitro group, is described. The scalable reaction sequence leads to the title compounds as important intermediates of pyrroloindoline alkaloids and related drugs in excellent yields and enantioselectivities. The synthesis of the hexahydrofurano[2,3‐b]indole skeleton, the spirocarbamate oxindole unit, and the formal synthesis of AG‐041R have been carried out to demonstrate the synthetic utility of this protocol. 相似文献
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Phosphine‐Catalyzed Enantioselective γ‐Addition of 3‐Substituted Oxindoles to 2,3‐Butadienoates and 2‐Butynoates: Use of Prochiral Nucleophiles 下载免费PDF全文
Tianli Wang Weijun Yao Fangrui Zhong Guo Hao Pang Prof. Dr. Yixin Lu 《Angewandte Chemie (International ed. in English)》2014,53(11):2964-2968
The first phosphine‐catalyzed enantioselective γ‐addition with prochiral nucleophiles and 2,3‐butadienoates as the reaction partners has been developed. Both 3‐alkyl‐ and 3‐aryl‐substituted oxindoles could be employed in this process, which is catalyzed by a chiral phosphine that is derived from an amino acid, thus affording oxindoles that bear an all‐carbon quaternary center at the 3‐position in high yields and excellent enantioselectivity. The synthetic value of these γ‐addition products was demonstrated by the formal total synthesis of two natural products and by the preparation of biologically relevant molecules and structural scaffolds. 相似文献