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1.
Morgan Hans Prof. Johan Wouters Prof. Albert Demonceau Prof. Lionel Delaude 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(29):9668-9676
Four zwitterions were prepared by treating 1,3‐dimesitylimidazolin‐2‐ylidene (SIMes) or 1,3‐dimesitylimidazol‐2‐ylidene (IMes) with either N‐tosyl benzaldimine or diphenylketene. They were isolated in high yields and characterized by IR and NMR spectroscopy. The molecular structures of three of them were determined by using X‐ray crystallography and their thermal stability was monitored by using thermogravimetric analysis. The imidazol(in)ium‐2‐amides were rather labile white solids that did not show any tendency to tautomerize into the corresponding 1,2,2‐triaminoethene derivatives. They displayed a mediocre catalytic activity in the Staudinger reaction of N‐tosyl benzaldimine with diphenylketene. In contrast, the imidazol(in)ium‐2‐enolates were orange‐red crystalline materials that remained stable over extended periods of time. Despite their greater stability, these zwitterions turned out to be efficient promoters for the model cycloaddition under scrutiny. As a matter of fact, their catalytic activity matched those recorded with the free carbenes. Altogether, these results provide strong experimental insight into the mechanism of the Staudinger reaction catalyzed by N‐heterocyclic carbenes. They also highlight the superior catalytic activity of the imidazole‐based carbene IMes compared with its saturated analogue SIMes in the reaction under consideration. 相似文献
2.
Phosphane‐Catalyzed [4+1] Annulation between Nitroalkenes and Morita–Baylis–Hillman Carbonates: Facile Synthesis of Isoxazoline N‐Oxides by Phosphorus Ylides
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A phosphane‐catalyzed [4+1] annulation between nitroalkenes and Morita–Baylis–Hillman carbonates has been realized; this provides facile and diastereoselective access to polysubstituted isoxazoline N‐oxides in moderate to excellent yields. In the annulation, an in situ formed allylic phosphorus ylide presumably serves as a pivotal active intermediate. This reaction accordingly represents the first example of phosphorus ylide initiated [4+1] cyclization of nitroalkenes to give isoxazoline N‐oxides. 相似文献
3.
Probing the Diastereoselectivity of Staudinger Reactions Catalyzed by N‐Heterocyclic Carbenes
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Morgan Hans Prof. Johan Wouters Prof. Albert Demonceau Prof. Lionel Delaude 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10870-10877
The reaction of ethylphenylketene with 1,3‐dimesitylimidazol‐2‐ylidene (IMes) or 1,3‐dimesitylimidazolin‐2‐ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions were fully characterized by various analytical techniques. Their thermal stabilities were monitored by thermogravimetric analysis and the molecular structure of SIMes ? EtPhC?C?O was determined by means of X‐ray crystallography. A mechanism was proposed to account for the trans‐diastereoselectivity observed in the [2+2] cycloaddition of ketenes and N‐protected imines catalyzed by N‐heterocyclic carbenes and an extensive catalytic screening was performed to test its validity. The steric bulk of the NHC catalyst markedly affected the cis/trans ratio of the model β‐lactam product. The nature of the solvent used to carry out the Staudinger reaction also significantly influenced its diastereoselectivity. Conversely, the nature of the substituent on the N‐sulfonated imine reagent and the reaction temperature were less critical parameters. 相似文献
4.
Enantioselective Nucleophilic β‐Carbon‐Atom Amination of Enals: Carbene‐Catalyzed Formal [3+2] Reactions
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Xingxing Wu Bin Liu Yuexia Zhang Martin Jeret Honglin Wang Pengcheng Zheng Prof. Song Yang Prof. Bao‐An Song Prof. Dr. Yonggui Robin Chi 《Angewandte Chemie (International ed. in English)》2016,55(40):12280-12284
An enantioselective β‐carbon amination for enals is disclosed. The nitrogen atom from a protected hydrazine with suitable electronic properties readily behaves as a nucleophile. Addition of the nitrogen nucleophile to a catalytically generated N‐heterocyclic‐carbene‐bound α,β‐unsaturated acyl azolium intermediate constructs a new carbon–nitrogen bond asymmetrically. The pyrazolidinone products from our catalytic reactions are common scaffolds in bioactive molecules, and can be easily transformed into useful compounds such as β3‐amino‐acid derivatives. 相似文献
5.
PPh3‐Catalyzed Ring‐Expansion Reactions of Sulfamate‐Derived Cyclic Imines with Acetylenedicarboxylates
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Zhilin Yang Hao Yu Lei Zhang Hang Wei Dr. Yumei Xiao Lanzhen Chen Dr. Hongchao Guo 《化学:亚洲杂志》2014,9(1):313-318
The PPh3‐catalyzed ring‐expansion reaction of sulfamate‐derived cyclic imines with acetylenedicarboxylates has been developed. The reaction works quite efficiently under very mild conditions to afford benzo[g][1,2,3]oxathiazocine‐4,5‐dicarboxylate 2,2‐dioxide derivatives in high yields. 相似文献
6.
Silver(I)‐Catalyzed Enantioselective [3+2]‐Cycloaddition Reaction of α‐Silylimines: A Facile Route to Quaternary‐Carbon‐Rich Scaffolds
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Dr. Naredla Kesava‐Reddy Christopher Golz Prof. Dr. Carsten Strohmann Dr. Kamal Kumar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(51):18373-18377
A silver‐catalyzed highly enantioselective 1,3‐dipolar cycloaddition reaction of α‐silylimines with pyrone‐based trisubstituted olefins was developed affording bi‐ and tricyclic α‐quaternary‐carbon‐rich pyrano‐pyrrolidines in excellent yields. The tricyclic benzopyrone adducts thus obtained were efficiently transformed into highly complex tetracyclic scaffolds supporting four consecutive stereogenic centers with three quaternary carbons. 相似文献
7.
Mechanism of Phosphine‐Catalyzed Allene Coupling Reactions: Advances in Theoretical Investigations
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Dr. Cheng‐Xing Cui Dr. Chunhui Shan Prof. Yu‐Ping Zhang Prof. Xiao‐Lan Chen Prof. Ling‐Bo Qu Prof. Yu Lan 《化学:亚洲杂志》2018,13(9):1076-1088
Organocatalysis has emerged as an effective strategy for chemical synthesis. Within this area, phosphine‐catalyzed coupling reactions have attracted considerable attention because of their versatility and wide range of applications in the construction of new C?C bonds. Recently, various experimental studies on the phosphine‐catalyzed coupling reaction of allenes have been reported, and mechanistic and computational studies have also progressed considerably. As a nucleophile, phosphine can react with an allene to form a zwitterionic phosphoniopropenide intermediate. After stepwise cycloaddition and proton transfer, the phosphine catalyst can be regenerated by C?P bond cleavage. Alternatively, the zwitterionic phosphoniopropenide intermediate could also be protonated by a Brønsted acid to generate a phosphonium intermediate, which can be used to construct new C?C bonds by electrophilic addition. In this review, we have summarized details of mechanistic studies of phosphine‐catalyzed allene coupling reactions that follow these two reaction modes. In addition to detailing the reaction pathway, the regioselectivity and diastereoselectivity of the phosphine‐catalyzed allene coupling reaction are also discussed in this review. 相似文献
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Rhodium(II)‐Catalyzed Intramolecular Annulation of 1‐Sulfonyl‐1,2,3‐Triazoles with Pyrrole and Indole Rings: Facile Synthesis of N‐Bridgehead Azepine Skeletons
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Jin‐Ming Yang Cheng‐Zhi Zhu Dr. Xiang‐Ying Tang Prof. Dr. Min Shi 《Angewandte Chemie (International ed. in English)》2014,53(20):5142-5146
A convenient and efficient synthetic method has been developed to construct highly functionalized N‐bridgehead azepine skeletons, which are of great importance in biological and pharmaceutical industry. The reaction proceeds through a rhodium(II) azavinyl carbene intermediate, which initiated the intramolecular C? H functionalization with pyrrolyl and indolyl rings. A variety of azepine derivatives were obtained in moderate to good yields under mild reaction conditions with high chemoselectivity. Several interesting derivatizations of the resulting products demonstrate that this method is synthetically valuable and useful. 相似文献
10.
A Phosphine‐Catalyzed Novel Asymmetric [3+2] Cycloaddition of C,N‐Cyclic Azomethine Imines with δ‐Substituted Allenoates
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Dr. De Wang Yu Lei Dr. Yin Wei Prof. Dr. Min Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15325-15329
Catalytic asymmetric [3+2] cycloadditions of C,N‐cyclic azomethine imines with δ‐substituted allenoates have been developed in the presence of (S)‐Me‐f‐KetalPhos, affording functionalized tetrahydroquinoline frameworks in good yields with high diastereo‐ and good enantioselectivities under mild condition. The substrate scope has been also examined. This is the first time that δ‐substituted allenoates have been applied as a δ,γ‐C?C bond participated C2 synthon in asymmetric synthesis. 相似文献
11.
Alkyl 2‐nitroethanoates react with alkyl propiolates in the presence of triphenylphosphine (Ph3P) in a mechanistically unprecedented reaction to afford tetraalkyl benzene‐1,2,3,5‐tetracarboxylates in moderate yields (36–42%). 相似文献
12.
Engaging Allene‐Derived Zwitterions in an Unprecedented Mode of Asymmetric [3+2]‐Annulation Reaction
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Dr. Muthukumar G. Sankar Dr. Miguel Garcia‐Castro Christopher Golz Prof. Dr. Carsten Strohmann Dr. Kamal Kumar 《Angewandte Chemie (International ed. in English)》2016,55(33):9709-9713
Catalytic addition of chiral phosphine, that is, (R)‐ or (S)‐SITCP, to an α‐substituted allene ester generated a zwitterionic dipole. Under optimized reaction conditions, this dipole could engage isatine‐derived N‐Boc‐ketimines in a novel mode of [3+2] annulation reaction. Pyrrolinyl spirooxindoles are thus afforded in high yields and with excellent enantioselectivities. The unprecedented annulation reaction successfully facilitated the construction of sp3‐rich and highly substituted 3,2′‐pyrrolidinyl spirooxindoles supporting many chiral centers. 相似文献
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14.
Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML
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Genoa R. Warner Matthew R. Mills Clarissa Enslin Shantanu Pattanayak Chakadola Panda Tamas Kumar Panda Prof. Sayam Sen Gupta Prof. Alexander D. Ryabov Prof. Terrence J. Collins 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(16):6226-6233
The catalytic activity of the N‐tailed (“biuret”) TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC6H3‐1,2‐( N COCMe2 N CO)2NR}Cl]2? ( 3 ; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a ); NO2, Me ( b ); H, Ph ( c )] in the oxidative bleaching of Orange II dye by H2O2 in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC6H3‐1,2‐( N COCMe2 N CO)2CMe2}OH2]? ( 1 ) and the more aggressive analogue [Fe(Me2C{CON(1,2‐C6H3‐4‐X) N CO}2)OH2]? ( 2 ). Catalysis by 3 of the reaction between H2O2 and Orange II (S) occurs according to the rate law found generally for TAML activators (v=kIkII[FeIII][S][H2O2]/(kI[H2O2]+kII[S]) and the rate constants kI and kII at pH 7 both decrease within the series 3 b > 3 a > 3 c . The pH dependency of kI and kII was investigated for 3 a . As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For kI, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a . For kII, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition kI?kII holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants ki for suicidal inactivation of the active forms of complexes 3 a – c were calculated using the general formula ln([S0]/[S∞])=(kII/ki)[FeIII]; here [FeIII], [S0], and [S∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of 3 c are also described. 相似文献
15.
Kseniya Revunova Dr. Georgii I. Nikonov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(3):839-845
Simple bases (KOtBu, KOH) catalyze the silane‐promoted reduction of ketones and esters to alcohols and of aldimines to amines. The inexpensive silane PMHS (polymethylhydrosiloxane) can be used as the reducing reagent. Double and triple bonds, as well as nitro‐ and cyano‐groups are tolerated. Careful dosing of the silane allows for chemoselective reduction of a more reactive group in the presence of a less reactive group (for example, aldehyde reduction in the presence of ketone/ketone reduction in the presence of ester group). Mechanistic studies showed that addition of base to silanes leads to silicate species, which are the acting reducing agents. Under basic conditions, hydrosiloxanes (tetramethyldisiloxane, TMDS; PMHS) convert into simple silanes (H2SiMe2, H3SiMe), making this a practical method to generate these challenging silanes. 相似文献
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17.
Li‐Jun Xiao Chao‐Yue Zhao Lei Cheng Bo‐Ya Feng Wei‐Min Feng Prof. Jian‐Hua Xie Prof. Xiu‐Fang Xu Prof. Qi‐Lin Zhou 《Angewandte Chemie (International ed. in English)》2018,57(13):3396-3400
A nickel(0)‐catalyzed hydroalkenylation of imines with styrene and its derivatives is described. A wide range of aromatic and aliphatic imines directly coupled with styrene and its derivatives, thus providing various synthetically useful allylic amines with up to 95 % yield. The reaction offers a new atom‐ and step‐economical approach to allylic amines by using alkenes instead of alkenyl‐metallic reagents. Experiments and DFT calculations showed that TsNH2 promotes the proton transfer from the coordinated olefin to the imine, accompanied by a new C?C bond formation. 相似文献
18.
Chuan‐Hu Lei Dr. De‐Xian Wang Dr. Liang Zhao Prof. Dr. Jieping Zhu Prof. Dr. Mei‐Xiang Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):16981-16987
Tandem reactions for the efficient synthesis of multifunctionalized 1,2,3,4‐tetrahydropyridines, 2,3‐dihydropyridin‐4(1H)‐ones, and pyridine derivatives have been developed and reaction mechanisms have been investigated. Synthetic cascades are initiated by the Zn(OTf)2‐mediated [5+1] cycloaddition of N‐formylmethyl‐substituted tertiary enamides to isocyanides, thus leading to the versatile heterocyclic enamino imine intermediates. Interception of the intermediates by diastereoselective reduction of imine functionality with Me4NBH(OAc)3 afforded 1,6‐disubstituted trans‐3‐hydroxy‐4‐arylamino‐ or ‐alkylamino‐1,2,3,4‐tetrahydropyridines, whereas acylation of the imino group followed by acidic hydrolysis produced 1,6‐disubstituted 3‐acyloxy‐2,3‐dihydropyridin‐4(1H)‐ones. Aerobic oxidation led to the aromatization followed by intermolecular acyl‐group transfer from the pyridinium nitrogen to the 3‐hydroxy moiety, thereby yielding substituted 3‐acyloxy‐4‐aminopyridines. Synthetic potentials of the resulting products have been demonstrated by expedient and highly stereoselective synthesis of cis,cis‐4,5‐dihydroxy‐2‐phenylpiperidine and trans,trans‐4‐amino‐5‐hydroxy‐2‐phenylpiperidine compounds, which are important in medicinal chemistry, through simple and practical reduction reactions. 相似文献
19.
A simple, environmental‐friendly, and practical method for the synthesis of benzodiazepine derivatives through a reaction of substituted o‐phenylenediamines with alkyl propiolates has been developed. The reactions generated the 1,5‐benzodiazepines in good to excellent yields in the presence of catalytic amount of In(OTf)3 under solvent‐free reaction conditions. 相似文献
20.
Pummerer‐type reaction intermediate 2 of α‐(methylthio)‐N‐methoxy‐N‐methyl acetamide (1) has been found to react with 1‐alkenes to afford ene adducts 3 . N‐Methoxy‐N‐methyl‐(E,E)‐2,4‐dienamides were synthesized from the adducts 3b‐f . 相似文献