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1.
Congjun Zhu Jie Dong Xueting Liu Liuzhou Gao Dr. Yue Zhao Prof. Dr. Jin Xie Prof. Dr. Shuhua Li Prof. Dr. Chengjian Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12917-12921
In this Communication, we report an unprecedented β-regioselective radical inverse hydroboration (compared with ionic hydroboration) of α,β-unsaturated amides with NHC-BH3 enabled by photoredox catalysis. Density functional theory (DFT) calculations show that the unique photoredox cycle is a key factor to control the β-regioselective radical hydroboration, by lowering the energy barrier in comparison with other pathways. This protocol provides a general and convenient route to construct a wide range of structurally diverse β-borylated amides in synthetically useful yields under mild conditions. 相似文献
2.
N. Chary Mamillapalli Prof. Govindasamy Sekar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18584-18588
Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral CuII/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)3SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)3SiH to afford the corresponding chiral β‐amino alcohol derivatives. 相似文献
3.
Dr. Qiang Liu Hong Yi Jie Liu Yuhong Yang Xu Zhang Ziqi Zeng Prof. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(16):5120-5126
Through the use of [Ru(bpy)3Cl2] (bpy=2,2′‐bipyridine) and [Ir(ppy)3] (ppy=phenylpyridine) as photocatalysts, we have achieved the first example of visible‐light photocatalytic radical alkenylation of various α‐carbonyl alkyl bromides and benzyl bromides to furnish α‐vinyl carbonyls and allylbenzene derivatives, prominent structural elements of many bioactive molecules. Specifically, this transformation is regiospecific and can tolerate primary, secondary, and even tertiary alkyl halides that bear β‐hydrides, which can be challenging with traditional palladium‐catalyzed approaches. The key initiation step of this transformation is visible‐light‐induced single‐electron reduction of C? Br bonds to generate alkyl radical species promoted by photocatalysts. The following carbon? carbon bond‐forming step involves a radical addition step rather than a metal‐mediated process, thereby avoiding the undesired β‐hydride elimination side reaction. Moreover, we propose that the Ru and Ir photocatalysts play a dual role in the catalytic system: they absorb energy from the visible light to facilitate the reaction process and act as a medium of electron transfer to activate the alkyl halides more effectively. Overall, this photoredox catalysis method opens new synthetic opportunities for the efficient alkenylation of alkyl halides that contain β‐hydrides under mild conditions. 相似文献
4.
Gold‐Catalyzed Highly Selective Photoredox C(sp2)−H Difluoroalkylation and Perfluoroalkylation of Hydrazones
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Dr. Jin Xie M. Sc. Tuo Zhang M. Sc. Fei Chen M. Sc. Nina Mehrkens Dr. Frank Rominger Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Angewandte Chemie (International ed. in English)》2016,55(8):2934-2938
The first gold‐catalyzed photoredox C(sp2)?H difluoroalkylation and perfluoroalkylation of hydrazones with readily available RF?Br reagents is reported. The resulting gem‐difluoromethylated and perfluoroalkylated hydrazones are highly functionalized, versatile molecules. A mild reduction of the coupling products can efficiently produce gem‐difluoromethylated β‐amino phosphonic acids and β‐amino acid derivatives. In mechanistic studies, a difluoroalkyl radical intermediate was detected by an EPR spin‐trapping experiment, indicating that a gold‐catalyzed radical pathway is operating. 相似文献
5.
Bhupal S. Karki Lalita Devi Ayushi Pokhriyal Ruchir Kant Namrata Rastogi 《化学:亚洲杂志》2019,14(24):4793-4797
A metal‐free, regioselective synthesis of trisubstituted pyrroles has been developed through a formal [3+2] cycloaddition reaction between 2H‐azirines and nitroalkenes under visible light/photoredox‐catalyzed conditions. The reaction proceeds through 2H‐azaallenyl radical addition on β‐nitrostyrenes in a Michael fashion followed by a base‐mediated denitration reaction. The directive group influence of the nitro group controls the regiochemistry of the reaction. 相似文献
6.
Dr. Marie Betou Dr. Louise Male Prof. Jonathan W. Steed Dr. Richard S. Grainger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(21):6505-6517
In an approach to the biologically important 6‐azabicyclo[3.2.1]octane ring system, the scope of the tandem 4‐exo‐trig carbamoyl radical cyclization—dithiocarbamate group transfer reaction to ring‐fused β‐lactams is evaluated. β‐Lactams fused to five‐, six‐, and seven‐membered rings are prepared in good to excellent yield, and with moderate to complete control at the newly formed dithiocarbamate stereocentre. No cyclization is observed with an additional methyl substituent on the terminus of the double bond. Elimination of the dithiocarbamate group gives α,β‐ or β,γ‐unsaturated lactams depending on both the methodology employed (base‐mediated or thermal) and the nature of the carbocycle fused to the β‐lactam. Fused β‐lactam diols, obtained from catalytic OsO4‐mediated dihydroxylation of α,β‐unsaturated β‐lactams, undergo semipinacol rearrangement via the corresponding cyclic sulfite or phosphorane to give keto‐bridged bicyclic amides by exclusive N‐acyl group migration. A monocyclic β‐lactam diol undergoes Appel reaction at a primary alcohol in preference to semipinacol rearrangement. Preliminary investigations into the chemo‐ and stereoselective manipulation of the two carbonyl groups present in a representative 7,8‐dioxo‐6‐azabicyclo[3.2.1]octane rearrangement product are also reported. 相似文献
7.
Visible‐Light‐Mediated Decarboxylation/Oxidative Amidation of α‐Keto Acids with Amines under Mild Reaction Conditions Using O2
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Jie Liu Dr. Qiang Liu Hong Yi Chu Qin Ruopeng Bai Xiaotian Qi Prof. Yu Lan Prof. Aiwen Lei 《Angewandte Chemie (International ed. in English)》2014,53(2):502-506
Photochemistry has ushered in a new era in the development of chemistry, and photoredox catalysis has become a hot topic, especially over the last five years, with the combination of visible‐light photoredox catalysis and radical reactions. A novel, simple, and efficient radical oxidative decarboxylative coupling with the assistant of the photocatalyst [Ru(phen)3]Cl2 is described. Various functional groups are well‐tolerated in this reaction and thus provides a new approach to developing advanced methods for aerobic oxidative decarboxylation. The preliminary mechanistic studies revealed that: 1) an SET process between [Ru(phen)3]2+* and aniline play an important role; 2) O2 activation might be the rate‐determining step; and 3) the decarboxylation step is an irreversible and fast process. 相似文献
8.
Promoted by AlCl3/Sm bimetallic system, α, β‐unsaturated ketones underwent reductive cyclodimerization to afford cyclopentanol derivatives under mild conditions. The reaction is stereocontrolled and regioselective over the competitive carbon‐carbon double bond reduction. 相似文献
9.
Dr. Xinjun Tang Prof. Dr. Armido Studer 《Angewandte Chemie (International ed. in English)》2018,57(3):814-817
Transition‐metal‐free radical α‐perfluoroalkylation with the accompanying vicinal β‐alkenylation of unactivated alkenes is presented. These radical cascades proceed by means of 1,4‐ or 1,5‐alkenyl migration by electron catalysis on readily accessed allylic alcohols. The reactions comprise a regioselective perfluoroalkyl radical addition with subsequent alkenyl migration and concomitant deprotonation to generate a ketyl radical anion that sustains the chain as a single‐electron‐transfer reducing reagent. 相似文献
10.
Masaki Shimoi Takashi Watanabe Prof. Katsuhiro Maeda Prof. Dennis P. Curran Dr. Tsuyoshi Taniguchi 《Angewandte Chemie (International ed. in English)》2018,57(30):9485-9490
Hydroboration of internal alkynes with N‐heterocyclic carbene boranes (NHC‐boranes) occurs to provide stable NHC (E)‐alkenylboranes upon thermolysis in the presence of di‐tert‐butyl peroxide. The E isomer results from an unusual trans‐hydroboration, and the E/Z selectivity is typically high (90:10 or greater). Evidence suggests that this hydroboration occurs by a radical‐chain reaction involving addition of an NHC‐boryl radical to an alkyne to give a β‐NHC‐borylalkenyl radical. Ensuing hydrogen abstraction from the starting NHC‐borane provides the product and returns the starting NHC‐boryl radical. Experiments suggest that the observed trans‐selectivity results from kinetic control in the hydrogen‐transfer reaction. 相似文献
11.
Hisham Ben Hamidane Aleksey Vorobyev Maud Larregola Aneta Lukaszuk Dirk Tourwé Dr. Solange Lavielle Philippe Karoyan Dr. Yury O. Tsybin Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4612-4622
We report on the characteristics of the radical‐ion‐driven dissociation of a diverse array of β‐amino acids incorporated into α‐peptides, as probed by tandem electron‐capture and electron‐transfer dissociation (ECD/ETD) mass spectrometry. The reported results demonstrate a stronger ECD/ETD dependence on the nature of the amino acid side chain for β‐amino acids than for their α‐form counterparts. In particular, only aromatic (e.g., β‐Phe), and to a substantially lower extent, carbonyl‐containing (e.g., β‐Glu and β‐Gln) amino acid side chains, lead to N? Cβ bond cleavage in the corresponding β‐amino acids. We conclude that radical stabilization must be provided by the side chain to enable the radical‐driven fragmentation from the nearby backbone carbonyl carbon to proceed. In contrast with the cleavage of backbones derived from α‐amino acids, ECD of peptides composed mainly of β‐amino acids reveals a shift in cleavage priority from the N? Cβ to the Cα? C bond. The incorporation of CH2 groups into the peptide backbone may thus drastically influence the backbone charge solvation preference. The characteristics of radical‐driven β‐amino acid dissociation described herein are of particular importance to methods development, applications in peptide sequencing, and peptide and protein modification (e.g., deamidation and isomerization) analysis in life science research. 相似文献
12.
Silke Erfle Sebastian Reimann Alina Bunescu Zharylkasyn A. Abilov Anke Spannenberg Peter Langer 《Helvetica chimica acta》2012,95(6):1037-1047
The TiCl4‐mediated [3+3] cyclocondensation of various 1,3‐bis(trimethylsilyloxy)buta‐1,3‐dienes with 1‐chloro‐1,1‐difluoro‐4‐(trimethylsilyloxy)pent‐3‐en‐2‐one provides a regioselective access to novel 6‐(chlorodifluoromethyl)salicylates (=6‐(chlorodifluoromethyl)‐2‐hydroxybenzoates) with very good regioselectivity. For selected products, it was demonstrated that the CF2Cl group can be transformed to CF2H and CF2(Allyl) by free‐radical reactions. 相似文献
13.
Yi Yang Gen Luo Youlin Li Xia Tong Mengmeng He Hongyao Zeng Yan Jiang Yingle Liu Yubin Zheng 《化学:亚洲杂志》2020,15(1):156-162
We report herein a facile synthetic method for converting unactivated (hetero)aryl electrophiles into β‐fluoroethylated (hetero)arenes via nickel‐catalyzed reductive cross‐couplings. This coupling reaction features the involvement of FCH2CH2 radical intermediate rather than β‐fluoroethyl manganese species which provides effective solutions to the problematic β‐fluoride side eliminations. The practical value of this protocol is further demonstrated by the late‐stage modification of several complex ArCl or ArOH‐derived bioactive molecules. 相似文献
14.
Oxydifluoromethylation of Alkenes by Photoredox Catalysis: Simple Synthesis of CF2H‐Containing Alcohols
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Yusuke Arai Ren Tomita Gaku Ando Dr. Takashi Koike Prof. Dr. Munetaka Akita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(4):1262-1265
We have developed a novel and simple protocol for the direct incorporation of a difluoromethyl (CF2H) group into alkenes by visible‐light‐driven photoredox catalysis. The use of fac‐[Ir(ppy)3] (ppy=2‐pyridylphenyl) photocatalyst and shelf‐stable Hu's reagent, N‐tosyl‐S‐difluoromethyl‐S‐phenylsulfoximine, as a CF2H source is the key to success. The well‐designed photoredox system achieves synthesis of not only β‐CF2H‐substituted alcohols but also ethers and an ester from alkenes through solvolytic processes. The present method allows a single‐step and regioselective formation of C(sp3)–CF2H and C(sp3)?O bonds from C=C moiety in alkenes, such as hydroxydifluoromethylation, regardless of terminal or internal alkenes. Moreover, this methodology tolerates a variety of functional groups. 相似文献
15.
The syntheses of well‐defined 7‐arm and 21‐arm poly(N‐isopropylacrylamide) (PNIPAM) star polymers possessing β‐cyclodextrin (β‐CD) cores were achieved via the combination of atom transfer radical polymerization (ATRP) and click reactions. Heptakis(6‐deoxy‐6‐azido)‐β‐cyclodextrin and heptakis[2,3,6‐tri‐O‐(2‐azidopropionyl)]‐β‐cyclodextrin, β‐CD‐(N3)7 and β‐CD‐(N3)21, precursors were prepared and thoroughly characterized by nuclear magnetic resonance and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. A series of alkynyl terminally functionalized PNIPAM (alkyne‐PNIPAM) linear precursors with varying degrees of polymerization (DP) were synthesized via atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide using propargyl 2‐chloropropionate as the initiator. The subsequent click reactions of alkyne‐PNIPAM with β‐CD‐(N3)7 and β‐CD‐(N3)21 led to the facile preparation of well‐defined 7‐arm and 21‐arm star polymers, namely β‐CD‐(PNIPAM)7 and β‐CD‐(PNIPAM)21. The thermal phase transition behavior of 7‐arm and 21‐arm star polymers with varying molecular weights were examined by temperature‐dependent turbidity and micro‐differential scanning calorimetry, and the results were compared to those of linear PNIPAM precursors. The anchoring of PNIPAM chain terminal to β‐CD cores and high local chain density for star polymers contributed to their considerably lower critical phase separation temperatures (Tc) and enthalpy changes during phase transition as compared with that of linear precursors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 404–419, 2009 相似文献
16.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(5):1391-1395
A general asymmetric route for the one‐step synthesis of chiral β‐branched amides is reported through the highly enantioselective isomerization of allylamines, followed by enamine exchange, and subsequent oxidation. The enamine exchange allows for a rapid and modular synthesis of various amides, including challenging β‐diaryl and β‐cyclic. 相似文献
17.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(40):12441-12444
The visible‐light‐promoted decarboxylation of α‐imino‐oxy propionic acids for the generation of iminyl radicals has been accomplished through the use of Ir(dFCF3ppy)2(dtbbpy)PF6 as a photoredox catalyst. Different from visible‐light‐promoted homolysis and single‐electron reduction of oxime derivatives, this strategy provides a novel catalytic cycle for alkene carboimination through a sequence comprising N‐radical generation, iminyl radical cyclization, intermolecular conjugate addition to a Michael acceptor, and single‐electron reduction to afford various pyrroline derivatives in an overall redox‐neutral process. The indolizidine alkaloid skeleton could be easily constructed from a pyrroline derivative prepared by this synthetic method. 相似文献
18.
Linli Zhang Zheng Wang Zhaobin Han Kuiling Ding 《Angewandte Chemie (International ed. in English)》2020,59(36):15565-15569
A Mn‐catalyzed diastereo‐ and enantioselective hydrogenation of α‐substituted β‐ketoamides has been realized for the first time under dynamic kinetic resolution conditions. anti‐α‐Substituted β‐hydroxy amides, which are useful building blocks for the synthesis of bioactive molecules and chiral drugs, were prepared in high yields with excellent selectivity (up to >99 % dr and >99 % ee) and unprecedentedly high activity (TON up to 10000). The origin of the excellent stereoselectivity was clarified by DFT calculations. 相似文献
19.
Songlin Zheng Zimin Chen Yuanyuan Hu Xiaoxiang Xi Zixuan Liao Weirong Li Weiming Yuan 《Angewandte Chemie (International ed. in English)》2020,59(41):17910-17916
A highly chemo‐ and regioselective intermolecular 1,2‐aryl‐aminoalkylation of alkenes by photoredox/nickel dual catalysis is described here. This three‐component conjunctive cross‐coupling is highlighted by its first application of primary alkyl radicals, which were not compatible in previous reports. The readily prepared α‐silyl amines could be transferred to α‐amino radicals by photo‐induced single electron transfer step. The radical addition/cross‐coupling cascade reaction proceeds under mild, base‐free and redox‐neutral conditions with good functional group tolerance, and importantly, provides an efficient and concise method for the synthesis of structurally valuable α‐aryl substituted γ‐amino acid derivatives motifs. 相似文献
20.
Novel Synthesis of 6‐Substituted 2‐Picolines from Aryl/heteroaryl β‐Enaminones and Meldrum's Acid Using CeCl3.7H2O/NaI
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One‐pot condensation of aryl/heteroaryl β‐enaminones, Meldrum's acid, and ammonium acetate in the presence of CeCl3.7H2O/NaI via tandem Michael addition–cyclodehydration–elimination sequence led to the formation of novel regioselective 6‐substituted 2‐picolines. 相似文献