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1.
Kinetic Resolution of Azomethine Imines by Brønsted Acid Catalyzed Enantioselective Reduction 下载免费PDF全文
Amanda Bongers Patrick J. Moon Prof. Dr. André M. Beauchemin 《Angewandte Chemie (International ed. in English)》2015,54(51):15516-15519
Azomethine imines are valuable substrates in asymmetric catalysis, and can be precursors to β‐amino carbonyl compounds and complex hydrazines. However, their utility is limited because complex and enantioenriched azomethine imines are often unavailable. Reported herein is a kinetic resolution of N,N′‐cyclic azomethine imines by enantioselective reduction (s=13–43). This resolution was accomplished using a Brønsted acid catalyst, and represents the first example of the asymmetric reduction of azomethine imines. The pyrazolidinone product (up to 86 % ee) and the recovered azomethine imine (up to 99 % ee) can both be used to access the opposite enantiomers of valuable products. 相似文献
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Liwen Fan Chunyu Han Xuerong Li Jiasheng Yao Zhengning Wang Chaochao Yao Weihao Chen Prof. Dr. Tao Wang Prof. Dr. Junfeng Zhao 《Angewandte Chemie (International ed. in English)》2018,57(8):2115-2119
The first enantioselective polyene cyclization initiated by a BINOL‐derived chiral N‐phosphoramide (NPA) catalyzed protonation of an imine is described. The ion‐pair formed between the iminium ion and chiral counter anion of the NPA plays an important role for controlling the stereochemistry of the overall transformation. This strategy offers a highly efficient approach to fused tricyclic frameworks containing three contiguous stereocenters, which are widely found in natural products. In addition, the first catalytic asymmetric total synthesis of (?)‐ferruginol was accomplished with an NPA catalyzed enantioselective polyene cyclization, as the key step for the construction of the tricyclic core, with excellent yield and enantioselectivity. 相似文献
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Gold(I)/Chiral Brønsted Acid Catalyzed Enantioselective Hydroamination–Hydroarylation of Alkynes: The Effect of a Remote Hydroxyl Group on the Reactivity and Enantioselectivity 下载免费PDF全文
Valmik S. Shinde Manoj V. Mane Dr. Kumar Vanka Arijit Mallick Dr. Nitin T. Patil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(3):975-979
The catalytic enantioselective hydroamination–hydroarylation of alkynes under the catalysis of (R3P)AuMe/(S)‐3,3′‐bis(2,4,6‐triisopropylphenyl)‐1,1′‐binaphthyl‐2,2′‐diyl hydrogenphosphate ((S)‐TRIP) is reported. The alkyne was reacted with a range of pyrrole‐based aromatic amines to give pyrrole‐embedded aza‐heterocyclic scaffolds bearing a quaternary carbon center. The presence of a hydroxyl group in the alkyne tether turned out to be very crucial for obtaining products in high yields and enantioselectivities. The mechanism of enantioinduction was established by carefully performing experimental and computational studies. 相似文献
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Brønsted Acid Enabled Nickel‐Catalyzed Hydroalkenylation of Aldehydes with Styrene and its Derivatives 下载免费PDF全文
Xing‐Wang Han Tao Zhang Yan‐Long Zheng Wei‐Wei Yao Jiang‐Fei Li You‐Ge Pu Prof. Dr. Mengchun Ye Qi‐Lin Zhou 《Angewandte Chemie (International ed. in English)》2018,57(18):5068-5071
A Brønsted acid enabled nickel‐catalyzed hydroalkenylation of aldehydes and styrene derivatives has been developed. The Brønsted acid acts as a proton shuttle to transfer a proton from the alkene to the aldehyde, thereby leading to an economical and byproduct‐free coupling. A series of synthetically useful allylic alcohols were obtained through one‐step reactions from readily available styrene derivatives and aliphatic aldehydes in up to 88 % yield and with high linear selectivity. 相似文献
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Iron/Brønsted Acid Catalyzed Asymmetric Hydrogenation: Mechanism and Selectivity‐Determining Interactions 下载免费PDF全文
Dr. Kathrin H. Hopmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):10020-10030
Hydrogenation catalysts involving abundant base metals such as cobalt or iron are promising alternatives to precious metal systems. Despite rapid progress in this field, base metal catalysts do not yet achieve the activity and selectivity levels of their precious metal counterparts. Rational improvement of base metal complexes is facilitated by detailed knowledge about their mechanisms and selectivity‐determining factors. The mechanism for asymmetric imine hydrogenation with Knölker’s iron complex in the presence of chiral phosphoric acids is here investigated computationally at the DFT‐D level of theory, with models of up to 160 atoms. The resting state of the system is found to be an adduct between the iron complex and the deprotonated acid. Rate‐limiting H2 splitting is followed by a stepwise hydrogenation mechanism, in which the phosphoric acid acts as the proton donor. C?H ??? O interactions between the phosphoric acid and the substrate are involved in the stereocontrol at the final hydride transfer step. Computed enantiomeric ratios show excellent agreement with experimental values, indicating that DFT‐D is able to correctly capture the selectivity‐determining interactions of this system. 相似文献
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Dr. Bo Peng Dr. Xueliang Huang Dr. Lan‐Gui Xie Prof. Dr. Nuno Maulide 《Angewandte Chemie (International ed. in English)》2014,53(33):8718-8721
A Brønsted acid catalyzed redox arylation of ynamides that employs aryl sulfoxides as the arylating agents is reported. This metal‐free transformation proceeds at room temperature and efficiently affords α‐arylated oxazolidinones in a redox‐neutral, atom‐economic fashion. 相似文献
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Shen Qu Dr. Mark D. Greenhalgh Andrew D. Smith 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(11):2816-2823
An operationally simple isothiourea-catalysed acylative kinetic resolution of unprotected 1,1′-biaryl-2,2′-diol derivatives has been developed to allow access to axially chiral compounds in highly enantioenriched form (s values up to 190). Investigation of the reaction scope and limitations provided three key observations: i) the diol motif of the substrate was essential for good conversion and high s values; ii) the use of an α,α-disubstituted mixed anhydride (2,2-diphenylacetic pivalic anhydride) was critical to minimize diacylation and give high selectivity; iii) the presence of substituents in the 3,3′-positions of the diol hindered effective acylation. This final observation was exploited for the highly regioselective acylative kinetic resolution of unsymmetrical biaryl diol substrates bearing a single 3-substituent. Based on the key observations identified, acylation transition state models have been proposed to explain the atropselectivity of this kinetic resolution. 相似文献
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Dr. Weijun Tang Steven Johnston Dr. Chaoqun Li Dr. Jonathan A. Iggo Dr. John Bacsa Prof. Jianliang Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(42):14187-14193
Asymmetric hydrogenation of imines leads directly to chiral amines, one of the most important structural units in chemical products, from pharmaceuticals to materials. However, highly effective catalysts are rare. This article reveals that combining an achiral pentamethylcyclopentadienyl (Cp*)–iridium complex with a chiral phosphoric acid affords a catalyst that allows for highly enantioselective hydrogenation of imines derived from aryl ketones, as well as those derived from aliphatic ones, with ee values varying from 81 to 98 %. A range of achiral iridium complexes containing diamine ligands were examined, for which the ligands were shown to have a profound effect on the reaction rate, enantioselectivity and catalyst deactivation. The chiral phosphoric acid is no less important, inducing enantioselection in the hydrogenation. The induction occurs, however, at the expense of the reaction rate. 相似文献
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Jun Kikuchi Masahiro Terada 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(25):8546-8550
An enantioselective intermolecular addition reaction of azlactones, as carbon nucleophiles, with styrene derivatives, as simple olefins, was demonstrated using a newly developed chiral Brønsted acid catalyst, namely, F10BINOL‐derived N‐triflyl phosphoramide. Addition products having vicinal tetrasubstituted carbon centers, one of which is an all‐carbon quaternary stereogenic center, were formed in good yields with moderate to high stereoselectivities. Extremely high acidity of the new chiral Brønsted acid was confirmed by its calculated pKa value based on DFT studies and is the key to accomplishing not only high catalytic activity but also efficient stereocontrol in the intermolecular addition. 相似文献
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Sandra Rodriguez Uxue Uria Efraim Reyes Luisa Carrillo Toms Tejero Pedro Merino Jose L. Vicario 《Angewandte Chemie (International ed. in English)》2020,59(17):6780-6784
The enantioselective synthesis of tropanols has been accomplished through chiral phosphoric acid catalyzed pseudotransannular ring opening of 1‐aminocyclohept‐4‐ene‐derived epoxides. The reaction proceeds together with the desymmetrization of the starting material and leads to the direct formation of the 8‐azabicyclo[3.2.1]octane scaffold with excellent stereoselectivity. The synthetic applicability of the reaction was demonstrated by the enantioselective synthesis of the two natural products (?)‐α‐tropanol and (+)‐ferruginine. 相似文献
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Masahiro Terada Prof. Dr. Kyoko Machioka Keiichi Sorimachi 《Angewandte Chemie (International ed. in English)》2009,48(14):2553-2556
An enriching experience : Chiral phosphoric acids have been used to catalyze the title transformation for aromatic and aliphatic hemiaminal ethers. The process affords the corresponding products in good to high enantioselectivity (see scheme; Boc=tert‐butoxycarbonyl, G=aromatic group). The method enables facile access to highly enantioenriched 1,3‐diamine derivatives.
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Asymmetric Brønsted Acid Catalyzed Substitution of Diaryl Methanols with Thiols and Alcohols for the Synthesis of Chiral Thioethers and Ethers 下载免费PDF全文
Adisak Chatupheeraphat Hsuan‐Hung Liao Steffen Mader Makoto Sako Prof. Dr. Hiroaki Sasai Dr. Iuliana Atodiresei Prof. Dr. Magnus Rueping 《Angewandte Chemie (International ed. in English)》2016,55(15):4803-4807
An enantioselective addition of thiols and alcohols to aza‐ortho‐quinone methides, starting from diaryl methanols, was developed. The asymmetric additions occur under mild reaction conditions in the presence of chiral phosphoric acids and furnish the corresponding adducts with excellent yields and enantioselectivities. 相似文献
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A General Access to Propargylic Ethers through Brønsted Acid Catalyzed Alkynylation of Acetals and Ketals with Trifluoroborates 下载免费PDF全文
Matthew Baxter Prof. Dr. Yuri Bolshan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(39):13535-13538
A general Brønsted acid catalyzed methodology for the alkynylation of acetals and ketals with alkynyltrifluoroborate salts has been developed. The reaction proceeds rapidly to afford valuable synthetic building block propargylic ethers in good to excellent yields. Unlike Lewis acid catalyzed transformations of trifluoroborates, this approach does not proceed via unstable organodifluoroborane intermediate. As a result, the developed methodology features excellent functional group tolerance and good atom economy. 相似文献