共查询到20条相似文献,搜索用时 46 毫秒
1.
Maria Kitamura Prof. Yoshimi Hirokawa Prof. Dr. Naoyoshi Maezaki Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(38):9911-9917
We have accomplished highly enantioselective [2,3]‐Wittig rearrangements of functionalized allyl benzyl ethers in the presence of a chiral di‐tBu‐bis(oxazoline) ligand. In various oxygenated benzylic ethers, the reactions proceeded with excellent diastereo‐ and enantioselectivities, although the presence of a methoxy substituent at the ortho‐position on the benzyl group drastically decreased the enantioselectivity. Conversely, o‐ethyl and o‐phenyl substituents had no significant effect on the selectivity. We found that the C2‐substituent of the allylic moiety played an important role in producing high enantioselectivity. Highly enantioselective [2,3]‐Wittig rearrangement in the presence of catalytic amounts of the chiral ligands is also described. 相似文献
2.
Copper‐Catalyzed Cyclization/aza‐Claisen Rearrangement Cascade Initiated by Ketenimine Formation: An Efficient Stereocontrolled Synthesis of α‐Allyl Cyclic Amidines
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Dr. Hua‐Dong Xu Zhi‐Hong Jia Ke Xu Mei Han Sai‐Nan Jiang Jing Cao Jia‐Cheng Wang Dr. Mei‐Hua Shen 《Angewandte Chemie (International ed. in English)》2014,53(35):9284-9288
An efficient and convenient synthesis of α‐allyl cyclic amidines has been achieved by applying a novel cascade reaction. Copper(I)‐mediated in situ N‐sulfonyl ketenimine formation from the reaction of a terminal alkyne with sulfonyl azide is followed by an intramolecular nucleophilic attack on the central carbon atom by an allylic tertiary amine, and then an aza‐Claisen rearrangement takes place through a chair transition state to furnish the titled amidines with complete stereocontrol. 相似文献
3.
Aza‐Quaternary Scaffolds from Selective Bond Cleavage of Bridgehead‐Substituted 7‐Azabicyclo[2.2.1]heptane: Total Synthesis of (+)‐Cylindricines C–E and (−)‐Lepadiformine A
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Prof. Dr. Ganesh Pandey Vaitla Janakiram 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(37):13120-13126
A novel bridgehead‐substituted aza‐bicyclic framework has been designed and developed in both enantiomeric forms through an asymmetric desymmetrization reaction. Strategic exploitation of the ring strain in the aza‐bicyclic framework has been utilized for the construction of the chiral aza‐quaterenary scaffolds by selective bond fragmentation processes. Furthermore, a strategically designed precursor is employed for selective bond cleavage to initiate a cascade rearrangement for the total synthesis of the 1‐azaspirotricyclic marine alkaloids (+)‐cylindricines C, D, and E, as well as (?)‐lepadiformine A. An oxidation/retro‐aldol/aza‐Michael sequence generated three new chiral centers with the required configuration in one pot. 相似文献
4.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(31):9345-9349
The first catalytic enantioselective asymmetric aza‐pinacol rearrangement is reported. The reactions are catalyzed by a chiral phosphoric acid and proceed via a highly organized transition state involving a cyclic aza‐ortho ‐xylylene intermediate to afford the indoline structures with good to excellent enantioselectivity. The synthetic utility of this method is demonstrated by the asymmetric synthesis of a key intermediate to the natural product minfiensine and the identification of a chiral lead compound to repress antibiotic resistance. 相似文献
5.
Qiong Tang Kai Fu Peiran Ruan Shunxi Dong Zhishan Su Xiaohua Liu Xiaoming Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(34):11972-11977
A highly enantioselective formal conjugate allyl addition of allylboronic acids to β,γ‐unsaturated α‐ketoesters has been realized by employing a chiral NiII/N,N′‐dioxide complex as the catalyst. This transformation proceeds by an allylboration/oxy‐Cope rearrangement sequence, providing a facile and rapid route to γ‐allyl‐α‐ketoesters with moderate to good yields (65–92 %) and excellent ee values (90–99 % ee). The isolation of 1,2‐allylboration products provided insight into the mechanism of the subsequent oxy‐Cope rearrangement reaction: substrate‐induced chiral transfer and a chiral Lewis acid accelerated process. Based on the experimental investigations and DFT calculations, a rare boatlike transition‐state model is proposed as the origin of high chirality transfer during the oxy‐Cope rearrangement. 相似文献
6.
Dr. Huilin Li Prof. Rongbiao Tong Prof. Jianwei Sun 《Angewandte Chemie (International ed. in English)》2016,55(48):15125-15128
An efficient organocatalytic enantioselective aza‐Piancatelli rearrangement is disclosed. The powerful process provides rapid access to valuable chiral 4‐amino‐2‐cyclopentenone building blocks from readily available 2‐furfurylcarbinols with excellent chemo‐, enantio‐, and diastereoselectivities under mild reaction conditions. 相似文献
7.
Palladium‐Catalyzed CH Activation of N‐Allyl Imines: Regioselective Allylic Alkylations to Deliver Substituted Aza‐1,3‐Dienes
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Prof. Dr. Barry M. Trost Dr. Subham Mahapatra Dr. Martin Hansen 《Angewandte Chemie (International ed. in English)》2015,54(20):6032-6036
A new mode of activation of an imine via a rare aza‐substituted π‐allyl complex is described. Palladium‐catalyzed C(sp3)? H activation of the N‐allyl imine and the subsequent nucleophilic attack by the α‐alkyl cyanoester produced the 1‐aza‐1,3‐diene as the sole regioisomer. In contrast, nucleophilic attack by the α‐aryl cyanoester exclusively delivered the 2‐aza‐1,3‐diene, which was employed in an inverse‐electron‐demand Diels–Alder reaction for heterobiaryl synthesis. 相似文献
8.
Prof. Dr. Hiromichi Fujioka Kenji Nakahara Naoyuki Kotoku Yusuke Ohba Yasushi Nagatomi Tsung‐Lung Wang Yoshinari Sawama Kenichi Murai Kie Hirano Tomohiro Oki Shintaro Wakamatsu Prof. Dr. Yasuyuki Kita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(43):13861-13870
A route for the asymmetric synthesis of (?)‐stenine, a member of the Stemona alkaloid family used as folk medicine in Asian countries, is described. The key features of the sequence employed include stereoselective transformations on a cyclohexane ring controlled by a chiral auxiliary unit and an intramolecular Mitsunobu reaction to construct the perhydroindole ring system. By using an intermediate in the route to (?)‐stenine, an asymmetric synthesis of 9a‐epi‐stenine was also executed. The C(9a) stereocenter in 9a‐epi‐stenine was installed by using a Staudinger/aza‐Wittig reaction of a keto–azide precursor followed by reduction of the resulting imine. The results of this effort demonstrate the applicability of the chiral auxiliary based strategy to the preparation of naturally occurring alkaloids that contain highly functionalized cyclohexane cores. 相似文献
9.
Nickel(II)‐Catalyzed Asymmetric Propargyl [2,3] Wittig Rearrangement of Oxindole Derivatives: A Chiral Amplification Effect
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Xi Xu Jianlin Zhang Prof. Dr. Shunxi Dong Prof. Dr. Lili Lin Xiaobin Lin Prof. Dr. Xiaohua Liu Prof. Dr. Xiaoming Feng 《Angewandte Chemie (International ed. in English)》2018,57(28):8734-8738
A highly enantioselective [2,3] Wittig rearrangement of oxindole derivatives was realized by using a chiral N,N′‐dioxide/NiII complex as the catalyst under mild reaction conditions. A strong chiral amplification effect was observed, and allowed access to chiral 3‐hydroxy 3‐substituted oxindoles bearing allenyl groups in high yields and enantioselectivities (up to 92 % ee) by using a ligand with only 15 % ee. A reasonable explanation was given based on the experimental investigations and X‐ray crystal structures of enantiomerically pure and racemic catalysts. Moreover, the first catalytic kinetic resolution of racemic oxindole derivatives by a [2,3] Wittig rearrangement was realized with high efficiency and stereoselectivity. 相似文献
10.
Daniel F. Fischer Dr. Assem Barakat Zhuo‐qun Xin Matthias E. Weiss René Peters Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(35):8722-8741
Systematic studies have been performed to develop highly efficient catalysts for the asymmetric aza‐Claisen rearrangement of trihaloacetimidates. Herein, we describe the stepwise development of these catalyst systems involving four different catalyst generations finally resulting in the development of a planar chiral pentaphenylferrocenyl oxazoline palladacycle. This complex is more reactive and has a broader substrate tolerance than all previously known catalyst systems for asymmetric aza‐Claisen rearrangements. Our investigations also reveal that subtle changes can have a big impact on the activity. With the enhanced catalyst activity, the asymmetric aza‐Claisen rearrangement has a very broad scope: the methodology not only allows the formation of highly enantioenriched primary allylic amines, but also secondary and tertiary amines; allylic amines with N‐substituted quaternary stereocenters are conveniently accessible as well. The reaction conditions tolerate many important functional groups, thus providing stereoselective access to valuable functionalized building blocks, for example, for the synthesis of unnatural amino acids. Our results suggest that face‐selective olefin coordination is the enantioselectivity‐determining step, which is almost exclusively controlled by the element of planar chirality. 相似文献
11.
《中国化学》2018,36(8):723-730
Phosphine‐relayed olefination and aza‐Wittig reactions of readily available aldehydes with 2,2,2‐trifluorodiazoethane (CF3CHN2) have been realized. This protocol enables the facile construction of a series of trifluoromethylated alkenes and hydrazones in good to high yield under mild conditions. 相似文献
12.
Highly Enantioselective Aza‐Michael Reaction between Alkyl Amines and β‐Trifluoromethyl β‐Aryl Nitroolefins
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Prof. Dr. Yong Huang 《Angewandte Chemie (International ed. in English)》2015,54(51):15414-15418
The aza‐Michael addition reaction is a vital transformation for the synthesis of functionalized chiral amines. Despite intensive research, enantioselective aza‐Michael reactions with alkyl amines as the nitrogen donor have not been successful. We report the use of chiral N‐heterocyclic carbenes (NHCs) as noncovalent organocatalysts to promote a highly selective aza‐Michael reaction between primary alkyl amines and β‐trifluoromethyl β‐aryl nitroolefins. In contrast to classical conjugate‐addition reactions, a strategy of HOMO‐raising activation was used. Chiral trifluoromethylated amines were synthesized in high yield (up to 99 %) with excellent enantioselectivity (up to 98 % ee). 相似文献
13.
3‐Iodoindole N‐carboximidamides and N‐carboximidoates 4 were prepared regioselectively via a sequential aza‐Wittig/iodine induced cyclization, starting from easily accessible 2‐alkynylphenyl iminophosphorane, isocyanates, various nucleophiles and iodine. 相似文献
14.
Makoto Shimizu Haruna Katsurayama Isao Mizota Yusong Zhu 《Journal of heterocyclic chemistry》2019,56(9):2479-2486
Synthesis of 2‐methyl‐3‐oxoindoline‐2‐carboxylates is developed using a bis(trimethylsilyl)aluminum chloride‐induced aza‐Brook rearrangement as a crucial step. Regarding the organoaluminum species, use of readily available tris(trimethylsilyl)aluminum·ether complex was not suitable for the present cyclization. After a series of examination of the reaction conditions, the aza‐Brook rearrangement and the subsequent cyclization with 2 equivalens of bis(trimethylsilyl)aluminum chloride were found to be the most effective. An application to the synthesis of a potential intermediate of duocarmycin A is also described, in which ozonolysis of the styrenyl moiety and the Barton–McCombie deoxygenation of the hydroxymethyl group were successfully carried out. 相似文献
15.
Thirteen new 2-alkylaminoimidazolones(4) wre rapidly synthesized by a new solution-phase parallel synthetic method,which includes aza-Wittig reaction of iminophosphorane(1) with aromatic isocyanate to give carbodi-imide(2) and subsequent reaction of 2 with various aliphatic primary amine in a parallel fashion.The products were confirmed by ^1H NMR,MS,IR and X-ray crystallographic analysis.The unusual selectivity of the cyclization was probably due to the deometry of the guanidine intermediate. 相似文献
16.
Regioselective Synthesis of 2‐Acylquinazolines and 3H‐1,4‐Benzodiazepin‐3‐ones by a Ugi 4CC/Staudinger/aza‐Wittig Sequence
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α‐Acylamino‐carboxamide azides 1 , obtained from Ugi reactions of o‐azidobenzaldehyde, amines, benzoylformic acid, and isocyanides, reacted with triphenylphosphine to give various 2‐acylquinazolines 3 and/or 3H‐1,4‐benzodiazepin‐3‐ones 4 in moderate to good yields via sequential Staudinger and intramolecular aza‐Wittig reaction. 相似文献
17.
Catalytic Asymmetric Piancatelli Rearrangement: Brønsted Acid Catalyzed 4π Electrocyclization for the Synthesis of Multisubstituted Cyclopentenones
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Dr. Yunfei Cai Dr. Yurong Tang Prof. Dr. Magnus Rueping 《Angewandte Chemie (International ed. in English)》2016,55(45):14126-14130
The first catalytic asymmetric Piancatelli reaction is reported. Catalyzed by a chiral Brønsted acid, the rearrangement of a wide range of furylcarbinols with a series of aniline derivatives provides valuable aminocyclopentenones in high yields as well as excellent enantioselectivities and diastereoselectivities. The high value of the aza‐Piancatelli rearrangement was demonstrated by the synthesis of a cyclopentane‐based hNK1 antagonist analogue. 相似文献
18.
The aza‐Wittig reaction of benzophenone‐ or acetophenone 1‐[(triphenylphosphoranylidene)amino]‐ethylidenehydrazone ( 4 ) with aromatic aldehydes provides a new route to 1,2,4‐triazoles 7 via the thermal reaction of the expected azinoimines 5. 相似文献
19.
Chloride‐bridged palladacycle dimers 1 have been evaluated as catalysts for the aza‐Claisen rearrangement of allylic imidates 2 to the corresponding allyl amides 3 . Cyclopalladated complexes 1b–e bearing electron‐donating substituents on imidazoline ring were identified as being superior catalysts because excellent yields were obtained without using silver salts for activation. In addition, a correlation between substituents on the imidazoline ring and catalytic activity of palladacycles was established. The electron‐deficient ligands and good solubility of catalysts in the reaction solution increase the catalytic activity. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
氮杂Wittig反应的最近进展 总被引:22,自引:2,他引:20
综述了最近几年氮杂Wittig反应的研究进展,包括分子间氮杂Wittig反应、分子内氮杂wittig反应及串联的氮杂Wittig反应。讨论了氮杂Wittig反应在一些含氮杂环、稠杂环及天然产物合成中的应用。 相似文献