共查询到20条相似文献,搜索用时 15 毫秒
1.
Matthew C. Leclerc Dr. Serge I. Gorelsky Bulat M. Gabidullin Ilia Korobkov Prof. R. Tom Baker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8063-8067
Selective reactions between nucleophilic N,N′‐diaryl‐heterocyclic carbenes (NHCs) and electrophilic fluorinated alkenes afford NHC fluoroalkenes in high yields. These stable compounds undergo efficient and selective fluoride abstraction with Lewis acids to give polyfluoroalkenyl imidazolium salts. These salts react at Cβ with pyrrolidine to give ammonium fluoride‐substituted salts, which give rise to conjugated imidazolium‐enamine salts through loss of HF. Alternatively, reaction with 4‐(dimethylamino)‐pyridine provides a Cα‐pyridinium‐substituted NHC fluoroalkene. These compounds were studied using multinuclear NMR spectroscopy, mass spectrometry, and X‐ray crystallography. Insight into their electronic structure and reactivity was gained through the use of DFT calculations. 相似文献
2.
Ivana Defrenza Alessia Catalano Alessia Carocci Antonio Carrieri Marilena Muraglia Antonio Rosato Filomena Corbo Carlo Franchini 《Journal of heterocyclic chemistry》2015,52(6):1705-1712
Starting from 2‐amino‐1,3‐mercaptobenzothiazoles recently reported ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h ), a series of the corresponding 2‐mercapto‐1,3‐benzothiazole isosters ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ) were screened for their in vitro antibacterial and antifungal activities. Results underline that the presence of the mercapto moiety at the 2‐position of the heterocyclic nucleus is crucial for activity against bacteria. The biological screening against Candida spp. identified commercial 2f as the most promising compound as antifungal against Candida albicans and tropicalis. Molecular modeling studies supported these results. Then, to enlarge structure‐activity relationship (SAR) studies on series 1 , newly synthesized compounds ( 1k , 1l , 1m , 1n , 1o , 1p ) were reported. All the compounds belonging to this series and bearing a bulky substituent at the 6‐position of the aryl moiety showed high antifungal activity. 相似文献
3.
Wojciech Kroszczyski Ewa Olszewska Piotr Saaski Janusz Jurczak 《Helvetica chimica acta》2004,87(6):1488-1492
A simple and effective method to deprotect of sterically hindered steroid esters is described. Deprotection was carried out in MeOH in the presence of a catalytic amount of Et3N under high‐pressure conditions. Enzymatic, anionite, and high‐pressure methods are compared. 相似文献
4.
Le' an Hu Yao Zhang Qing‐Wen Zhang Qin Yin Xumu Zhang 《Angewandte Chemie (International ed. in English)》2020,59(13):5321-5325
A Ru‐catalyzed direct asymmetric reductive amination of ortho‐OH‐substituted diaryl and sterically hindered ketones with ammonium salts is reported. This method represents a straightforward route toward the synthesis of synthetically useful chiral primary diarylmethylamines and sterically hindered benzylamines (up to 97 % yield, 93–>99 % ee). Elaborations of the chiral amine products into bioactive compounds and a chiral ligand were demonstrated through manipulation of the removable and convertible ‐OH group. 相似文献
5.
Pyrene‐Based Bisazolium Salts: From Luminescence Properties to Janus‐Type Bis‐N‐Heterocyclic Carbenes 下载免费PDF全文
Sergio Gonell Dr. Macarena Poyatos Prof. Eduardo Peris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9716-9724
A series of pyrene‐based bisazolium salts have been obtained starting from 4,5,9,10‐tetrabromo‐2,7‐di‐tert‐butylpyrene. The synthetic procedure to the pyrene‐bisazoliums (PBIs) reveals an unexpected behavior, as a consequence of the presence of the alkyl groups (alkyl=Me, Et, n‐Pr, and n‐Bu) coming from the trisalkoxyformate in the final products, instead of the expected tBu of tAmyl groups from the starting tetra‐aminated pyrenes. All bisazoliums show fluorescence properties, with emissions in the range of 370–420 nm, and quantum yields ranging from 0.29 to 0.41. The PBIs were used as bis‐NHC precursors in the preparation of a series of dirhodium and diiridium complexes, which have been fully characterized. The electrochemical studies on selected dimetallic complexes reveal that the electronic communication between the metals through the polyaromatic linker is negligible. 相似文献
6.
Galkina I. V. Andriyashin V. V. Romanov S. R. Davletshin R. R. Pozdeev O. K. Shulaeva M. P. Litvinov I. A. Bakhtiyarova Yu. V. 《Russian Journal of General Chemistry》2022,92(7):1199-1207
Russian Journal of General Chemistry - A procedure was developed for the synthesis of quaternary phosphonium salts with two phosphorus atoms [P(III) and P(V)] based on phosphorylated hindered... 相似文献
7.
《中国化学会会志》2017,64(4):420-426
Six new silver complexes containing symmetrical N ‐heterocyclic carbene (NHC ) ligands were synthesized by the reaction of azolium salts with Ag2O in CH2Cl2 . These complexes were tested against Gram‐negative bacterial strains (Escherichia coli and Pseudomonas aeruginosa ), Gram‐positive bacterial strains (Enterococcus faecalis and Staphylococcus aureus ), and fungal strains (Candida albicans and Candida tropicalis ), and all tested complexes showed good activity against the different microorganisms. 相似文献
8.
Dr. N. Kodiah Beyeh Dr. Fangfang Pan Dr. Sandip Bhowmik Toni Mäkelä Prof. Robin H. A. Ras Acad. Prof. Kari Rissanen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(4):1355-1361
N‐Alkyl ammonium resorcinarene salts (NARYs, Y=triflate, picrate, nitrate, trifluoroacetates and NARBr) as tetravalent receptors, are shown to have a strong affinity for chlorides. The high affinity for chlorides was confirmed from a multitude of exchange experiments in solution (NMR and UV/Vis), gas phase (mass spectrometry), and solid‐state (X‐ray crystallography). A new tetra‐iodide resorcinarene salt (NARI) was isolated and fully characterized from exchange experiments in the solid‐state. Competition experiments with a known monovalent bis‐urea receptor ( 5 ) with strong affinity for chloride, reveals these receptors to have a much higher affinity for the first two chlorides, a similar affinity as 5 for the third chloride, and lower affinity for the fourth chloride. The receptors affinity toward chloride follows the trend K1?K2?K3≈ 5 >K4, with Ka=5011 m ?1 for 5 in 9:1 CDCl3/[D6]DMSO. 相似文献
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11.
《Angewandte Chemie (International ed. in English)》2017,56(4):1135-1140
The reaction of the 2‐(trimethylsilyl)imidazolium triflate 9 with diarylboron halides (4‐R‐C6H4)2BX (R=H, X=Br; R=CH3, X=Cl; R=CF3, X=Cl) afforded the NHC‐stabilized borenium cations 10 a – c . Cyclic voltammetry revealed a linear correlation between the Hammett parameter σ p of the para substituent and the half‐wave potential. Chemical reduction with decamethylcobaltocene, [(C5Me5)2Co], furnished the corresponding radicals 11 a – c ; their characterization by EPR spectroscopy confirmed the paramagnetic character of 11 a – c , with large hyperfine coupling constants to the boron isotopes 11B and 10B, while delocalization of the unpaired electron into the NHC is negligible. DFT calculations of the percentage of spin density distribution between the carbene (NHC) and the boryl fragments (BR2) revealed for 11 a – c a spin density ratio (BR2/NHC) of ca. 9:1, which underlines their distinct boryl radical character. The molecular structure of the most stable species 11 c was established by X‐ray diffraction analysis. 相似文献
12.
Prof. Javier Ruiz Lucía García Dr. Marilín Vivanco Ángela Berros Dr. Juan Francisco Van der Maelen 《Angewandte Chemie (International ed. in English)》2015,54(14):4212-4216
By means of a combined experimental and theoretical approach, the electronic features and chemical behavior of metalla‐N‐heterocyclic carbenes (MNHCs, N‐heterocyclic carbenes containing a metal atom within the heterocyclic skeleton) have been established and compared with those of classical NHCs. MNHCs are strongly basic (proton affinity and pKa values around 290 kcal mol?1 and 36, respectively) with a narrow singlet–triplet gap (around 23 kcal mol?1). MNHCs can be generated from the corresponding metalla‐imidazolium salts and trapped by addition of transition‐metal complexes affording the corresponding heterodimetallic dicarbene derivatives, which can serve as carbene transfer agents. 相似文献
13.
A new series of bis‐N‐heterocyclic carbene precursors, LHX ( 3a–d ), have been synthesized and characterized by appropriate spectroscopic techniques and microanalyses. In situ prepared Pd(OAc)2/bis‐N‐heterocyclic carbene precursors catalysts have catalyzed unactivated aryl chlorides on the Suzuki cross‐coupling reaction under mild reaction conditions in aqueous media. 相似文献
14.
Yoshihito Kayaki Dr. Masafumi Yamamoto Takao Ikariya Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(23):4194-4197
Getting a fix : N‐heterocyclic carbenes (NHCs) and NHC–CO2 adducts serve as potent organocatalysts for carbonate synthesis by the addition of a CO2 unit to propargylic alcohols or epoxides under mild and solvent‐free reaction conditions (see scheme). The enhanced Lewis basicity of imidazol‐2‐ylidenes bearing electron‐donating alkyl groups on the nitrogen atoms leads to utilizing CO2 as a nucleophilic fragment in the chemical fixation processes.
15.
Rajendra S. Ghadwal Herbert W. Roesky Prof. Dr. Dr. h.c. Regine Herbst‐Irmer Peter G. Jones 《无机化学与普通化学杂志》2009,635(3):431-433
N‐Heterocyclic carbene adducts of aluminium triiodide, IMes · AlI3 ( 1 ) and IPr · AlI3 ( 2 ) (IMes = 1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene and IPr = 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) are reported. These adducts are available by the reaction of aluminium triiodide with the correspondingN‐heterocyclic carbene. Compounds 1 and 2 are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterised by elemental analysis, NMR spectroscopy and single‐crystal X‐ray diffraction studies. 相似文献
16.
The synthesis and reactivity of mono‐ and bis‐S‐xanthyl NHC‐boranes is reported. The new NHC‐boranes are prepared through nucleophilic exchange at boron from either mono‐ or bis‐triflyl NHC‐boranes, themselves obtained by protolysis of the NHC‐BH3 starting compounds. The B?H bond of the S‐xanthyl NHC‐boranes can be cleaved both homolytically and heterolytically, albeit the latter is more synthetically useful. The S‐xanthyl NHC‐boranes can reduce both aldehydes and imines. The B?S bond can also be cleaved homolytically. Under UV irradiation, the S‐xanthyl NHC‐boranes generate NHC‐boryl radicals that can initiate radical polymerizations of acrylates. 相似文献
17.
Dr. Ahmad El‐Hellani Prof. Vincent Lavallo 《Angewandte Chemie (International ed. in English)》2014,53(17):4489-4493
Here we describe the fusion of two families of unusual carbon‐containing molecules that readily disregard the tendency of carbon to form four chemical bonds, namely N‐heterocyclic carbenes (NHCs) and carborane anions. Deprotonation of an anionic imidazolium salt with lithium diisopropylamide at room temperature leads to a mixture of lithium complexes of C‐2 and C‐5 dianionic NHC constitutional isomers as well as a trianionic (C‐2, C‐5) adduct. Judicious choice of the base and reaction conditions allows the selective formation of all three stable polyanionic carbenes. In solution, the so‐called abnormal C‐5 NHC lithium complex slowly isomerizes to the normal C‐2 NHC, and the process can be proton‐catalyzed by the addition of the anionic imidazolium salt. These results indicate that the combination of two unusual forms of carbon atoms can lead to unexpected chemical behavior, and that this strategy paves the way for the development of a broad new generation of NHC ligands for catalysis. 相似文献
18.
Lorenzo Di Marco Dr. Morgan Hans Prof. Lionel Delaude Dr. Jean‐Christophe M. Monbaliu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4508-4514
Two methods were assessed for the generation of common N‐heterocyclic carbenes (NHCs) from stable imidazol(in)ium precursors using convenient and straightforward continuous‐flow setups with either a heterogeneous inorganic base (Cs2CO3 or K3PO4) or a homogeneous organic base (KN(SiMe3)2). In‐line quenching with carbon disulfide revealed that the homogeneous strategy was most efficient for the preparation of a small library of NHCs. The generation of free nucleophilic carbenes was next telescoped with two benchmark NHC‐catalyzed reactions; namely, the transesterification of vinyl acetate with benzyl alcohol and the amidation of N‐Boc‐glycine methyl ester with ethanolamine. Both organocatalytic transformations proceeded with total conversion and excellent yields were achieved after extraction, showcasing the first examples of continuous‐flow organocatalysis with NHCs. 相似文献
19.
Photochemical Carbopyridylation of Alkenes Using N‐Alkenoxypyridinium Salts as Bifunctional Reagents
Gangadhar Rao Mathi Yujin Jeong Yonghoon Moon Sungwoo Hong 《Angewandte Chemie (International ed. in English)》2020,59(5):2049-2054
N‐Alkenoxypyridinium salts have been used as synthons for the umpolung reaction of enolates for the preparation of α‐functionalized carbonyl compounds. In contrast, we found that the photoreduction of N‐alkenoxypyridinium salts generates α‐carbonyl radicals after cleavage of the N?O bond, thereby allowing simultaneous incorporation of α‐keto and pyridyl groups across unactivated alkenes. In the process, the formed α‐carbonyl radicals engage unactivated alkenes to afford alkyl radical intermediates poised for subsequent addition to pyridinium salts, which ultimately affords a variety of γ‐pyridyl ketones under mild reaction conditions. This transformation is characterized by a broad substrate scope and good functional‐group compatibility, and the utility of this transformation was further demonstrated by the late‐stage functionalization of complex biorelevant molecules. 相似文献
20.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(33):10038-10041
Discovered by Hawthorne in 1965, dicarbollide ions are an intriguing class of nido ‐carboranes that mimic the behavior of the cyclopentadienyl anion. Herein, we show that it is possible to directly link the dicarbollide ion to an N‐heterocyclic carbene (NHC) to form an isolable N‐dicarbollide‐substituted NHC dianion. This molecule can be accessed by the sequential double deprotonation of a mono‐nido ‐carboranyl imidazolium zwitterion. As revealed by a single‐crystal X‐ray diffraction study, the first deprotonation leads to a monoanionic dicarbollide ion that adopts a bis(dicarbollide) structure in the solid state. Subsequent deprotonation of this monoanion leads to the first N‐dicarbollide NHC, which was fully characterized by multinuclear NMR spectroscopy as well as single‐crystal X‐ray diffraction. 相似文献