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1.
Dr. Janakiram Vaitla Yannick T. Boni Prof. Dr. Huw M. L. Davies 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(19):7467-7472
Regio- and stereoselective distal allylic/benzylic C−H functionalization of allyl and benzyl silyl ethers was achieved using rhodium(II) carbenes derived from N-sulfonyltriazoles and aryldiazoacetates as carbene precursors. The bulky rhodium carbenes led to highly site-selective functionalization of less activated allylic and benzylic C−H bonds even in the presence of electronically preferred C−H bonds located α to oxygen. The dirhodium catalyst Rh2(S-NTTL)4 is the most effective chiral catalyst for triazole-derived carbene transformations, whereas Rh2(S-TPPTTL)4 works best for carbenes derived from aryldiazoacetates. The reactions afford a variety of δ-functionalized allyl silyl ethers with high diastereo- and enantioselectivity. The utility of the present method was demonstrated by its application to the synthesis of a 3,4-disubstituted l -proline scaffold. 相似文献
2.
Janakiram Vaitla Yannick T. Boni Huw M. L. Davies 《Angewandte Chemie (International ed. in English)》2020,59(19):7397-7402
Regio‐ and stereoselective distal allylic/benzylic C?H functionalization of allyl and benzyl silyl ethers was achieved using rhodium(II) carbenes derived from N‐sulfonyltriazoles and aryldiazoacetates as carbene precursors. The bulky rhodium carbenes led to highly site‐selective functionalization of less activated allylic and benzylic C?H bonds even in the presence of electronically preferred C?H bonds located α to oxygen. The dirhodium catalyst Rh2(S‐NTTL)4 is the most effective chiral catalyst for triazole‐derived carbene transformations, whereas Rh2(S‐TPPTTL)4 works best for carbenes derived from aryldiazoacetates. The reactions afford a variety of δ‐functionalized allyl silyl ethers with high diastereo‐ and enantioselectivity. The utility of the present method was demonstrated by its application to the synthesis of a 3,4‐disubstituted l ‐proline scaffold. 相似文献
3.
Ankur Kanti Guha 《Journal of organometallic chemistry》2011,696(2):586-593
A systematic density functional investigation has been carried out on the structure, stability and reactivity of heterocyclic carbenes of diverse flexibility, i.e., carbenes with different modes of binding specially normal and remote mode of binding. Ligating properties of these carbenes have been assessed by virtue of their HOMO energies and verified further by inspection of the symmetric CO frequencies of their respective palladium carbonyl complexes. All the remote carbenes were found to have higher σ-donating abilities compared to their normal analogs. N-heterocyclic carbenes 1 and 5 are found to be electrophilic in nature while the remote carbene 3 and P-heterocyclic carbene 6 are found to be nucleophilic. Quantum theory of atoms in molecules (QTAIM) reveals significant covalent character in the Ccarbene-Pd bonds. 相似文献
4.
This review reports the reactivity of carbenes (>C : ), both N‐heterocyclic and simpler ones, with 29 small molecules to form C–X bonds and some weak interactions. The structures thus obtained belong to many functional groups proving the characteristic reactivity of N‐heterocyclic carbenes. Particular attention has been paid to X‐ray structures that are useful for theoretical calculations. 相似文献
5.
Thermally-reversible covalent polymers featuring dynamic carbon-carbon double bonds and tunable molecular weights were prepared from difunctional carbenes; addition of transition metal complexes to these materials afforded the respective main-chain organometallic polymers. 相似文献
6.
Are Copper(I) Carbenes Capable Intermediates for Cyclopropanations? The Case for Ylide Intermediates
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Dr. Jamal T. Aldajaei Dr. James R. Keeffe Christopher A. Swift Dr. Scott Gronert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(36):12702-12708
A novel approach is used to synthesize a stable, ligated copper(I) carbene in the gas phase that is capable of typical metal carbenoid chemistry. However, it is shown that copper(I) carbenes generally undergo rapid unimolecular rearrangements including insertions into copper‐ligand bonds and Wolff rearrangements. The results indicate that most copper(I) carbenes are inherently unstable and would not be viable intermediates in condensed‐phase applications; an alternative intermediate that is less prone to rearrangements is required. Computational data suggest that ylides formed by the complexation of the carbene with solvent or other weak nucleophiles are viable intermediates in the reactions of copper(I) carbenes. 相似文献
7.
A new two-dimensional classification of singlet carbenes based on the difference in reactivity of their insertion reactions into the C-H bonds of acetonitrile and isobutane is presented. This classification combines the stability and the philicity of divalent species. Until now all of the experimentally based philicity scales are based on the addition to alkenes. Moreover, a new terminology for describing the reactivity of carbenes is introduced. Among the alkyl carbenes, acetyl carbene (2) and cyclopentadienylidene are shown as highly reactive electrophilic carbenes, whereas the other alkylidenes and alkenylidenes investigated are all less active than 2 and more nucleophilic. The stabilized-nucleophilic bicyclo[2.1.1]hex-2-en-5-ylidene (13) possesses a stability similar to that of cyclic alkyl amino carbene (CAAC) 18 and aminophosphoniocarbene 7. Strong hydrogen bridging is found between a C-H bond of acetonitrile and the nucleophilic carbenes 13 and 14. 相似文献
8.
Zhen Yang Yujing Guo Prof. Dr. Rene M. Koenigs 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6703-6706
Sigmatropic rearrangement reactions constitute one of the most fundamental reactions of carbenes. While state-of-the-art synthetic methods require the use of expensive precious metal catalysts, the application of visible light for the photolysis of α-aryldiazoacetates is much less investigated and provides an operationally simple entry to carbenes under mild reaction conditions. Herein, we report on blue-light induced sigmatropic rearrangement reactions of sulfur compounds with α-aryldiazoacetates. This process, depending on the substitution pattern of the sulfide, opens up formal insertion reactions of carbenes into S−N, S−C, or C−H bonds. 相似文献
9.
Xin Liu Li-Gao Liu Can-Ming Chen Xiao Li Prof. Dr. Zhou Xu Prof. Dr. Xin Lu Dr. Bo Zhou Prof. Dr. Long-Wu Ye 《Angewandte Chemie (International ed. in English)》2023,62(10):e202216923
[2,3]-Sigmatropic rearrangement reaction involving sulfonium ylide (Doyle–Kirmse reaction) generated from metal carbenes represents one of the powerful methods for the construction of C(sp3)−S and C−C bonds. Although significant advances have been achieved, the asymmetric versions via the generation of sulfonium ylides from metal carbenes have been rarely reported to date, and they have so far been limited to diazo compounds as metal carbene precursors. Here, we describe a copper-catalyzed enantioselective Doyle–Kirmse reaction via azide-ynamide cyclization, leading to the practical and divergent assembly of an array of chiral [1,4]thiazino[3,2-b]indoles bearing a quaternary carbon stereocenter in generally moderate to excellent yields and excellent enantioselectivities. Importantly, this protocol represents a unique catalytic asymmetric Doyle–Kirmse reaction via a non-diazo approach and an unprecedented asymmetric [2,3]-sigmatropic rearrangement via α-imino metal carbenes. 相似文献
10.
James E. Jackson George B. Mock Merry L. Tetef Guo-xiu Zheng Maitland Jones 《Tetrahedron》1985,41(8):1453-1464
Dicarbomethoxycarbene and dichlorocarbene add to 1,2,2-trimethylbicyclo[1.1.0]butanc in such a fashion as to suggest a concerted addition in which the central and side bonds are cleaved simultaneously. MNDO calculations support such a pathway and suggest that endo attack on the bicyclobutane is preferred to exo. Reaction of the same two carbenes with quadricyclane gives substituted derivatives of the exo-tricyclo[3.2.1.02,4]oct-6-ene system. Although these products rearrange further under the conditions of reaction and/or analysis, they can be shown to be primary products. It is suggested that quadricyclane reacts with carbenes in a concerted fashion. 相似文献
11.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(34):10261-10265
Fischer and Schrock carbenes display highly deshielded carbon chemical shifts (>250 ppm), in particular Fischer carbenes (>300 ppm). Orbital analysis of the principal components of the chemical shift tensors determined by solid‐state NMR spectroscopy and calculated by a 2‐component DFT method shows specific patterns that act as fingerprints for each type of complex. The calculations highlight the role of the paramagnetic term in the shielding tensor especially in the two most deshielded components (σ11 and σ22). The paramagnetic term of σ11 is dominated by coupling σ(M=C) with π*(M=C) through the angular momentum operator perpendicular to the σ and π M=C bonds. The highly deshielded carbon of Fischer carbenes results from the particularly low‐lying π*(M=C) associated with the CO ligand. A contribution of the coupling of π(M=C) with σ*(M=C) is found for Schrock and Ru‐based carbenes, indicating similarities between them, despite their different electronic configurations (d0 vs. d6). 相似文献
12.
Dr. Xin Zhang Dr. Yanbo Mei Prof. Dr. Liu Leo Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(63):e202202102
Aluminylenes (R−Al) are aluminium analogs of carbenes. In contrast to isolable carbenes, aluminylenes are extremely rare species. In the past years, pioneered by Schnöckel, Roesky and Power, a few free aluminylenes and their complexes have been reported. Such compounds have the aluminium atom in the oxidation state +I, which contrasts with classical organoaluminium derivatives that contain the element in the +III oxidation state. Aluminylenes, either in their free state or in the coordination sphere of a Lewis base, are capable of coordinating to transition metals and activating inert chemical bonds. Free aluminylenes are emerging as potent synthetic platforms for unusual aluminium species. 相似文献
13.
Prof. Dr. Holger Braunschweig Dr. William C. Ewing Dr. K. Geetharani Marius Schäfer 《Angewandte Chemie (International ed. in English)》2015,54(5):1662-1665
The first examples of adducts of cyclic alkyl(amino) carbenes (CAAC) and N‐heterocyclic carbenes (NHCs) with iminoboranes have been synthesized and isolated at low temperature (?45 °C). The adducts show short B?N bonds and planarity at boron, mimicking the structures of the isoelectronic imine functionality. When di‐tert‐butyliminoborane was reacted with 1,3‐bis(isopropyl)imidazol‐2‐ylidene (IPr), the initially formed Lewis acid–base adduct quickly rearranged to form a new carbene substituted with an aminoborane at the 4‐position. Warming the iminoborane–CAAC adduct to room temperature resulted in an intramolecular cyclization to give a bicyclic 1,2‐azaborilidine compound. 相似文献
14.
Barluenga J Fernández-Rodríguez MA Andina F Aguilar E 《Journal of the American Chemical Society》2002,124(37):10978-10979
The reaction of strained bicyclic olefins with alkynyl carbenes and terminal olefins involves the creation of five new sigma C-C bonds with the concomitant formation of two new rings, thus creating a complex and densely functionalized structure in a single operation. 相似文献
15.
《Journal of organometallic chemistry》2005,690(24-25):5867-5875
In order to probe the ligand properties we have examined a series of Cr(CO)5L and Ni(CO)3L complexes using density functional theory (DFT). The ligands included in our study are N-heterocyclic carbenes (NHCs) and Bertrand-type carbenes. Our study shows that the carbene–metal bonds of imidazol-2-ylidenes (1), imidazolin-2-ylidenes (2), thiazo-2-ylidenes (3), and triazo-5-ylidenes (4) are significantly stronger than those of Bertrand-type carbenes (5–7). The force constants of C–O in complexes are related to the property of isolated carbenes such as proton affinity (PA), electronegativity (χ), and charge transfer (ΔN). NHCs and Bertrand-type carbenes are identified as nucleophilic, soft ligands. Carbene stabilization energy (CSE) computations indicate that carbenes 1 and 4 are the most stable species, while 2 and 3 are less stable. In contrast to NHCs, CSE of carbenes 5–7 are much smaller, and their relative stabilities are in the order (amino)(aryl) carbenes 7e–7g > (amino)(alkyl) carbenes 7a–7d > (phosphino)(aryl) 6d–6e, and (phosphino)(silyl) carbenes 5a–5c > (phosphino)(alkyl) carbenes 6a–6c. 相似文献
16.
Jacquet O Das Neves Gomes C Ephritikhine M Cantat T 《Journal of the American Chemical Society》2012,134(6):2934-2937
A highly active organocatalytic system based on N-heterocyclic carbenes has been designed for the formylation of N-H bonds in a large variety of nitrogen molecules and heterocycles, using two chemical wastes: CO(2) and polymethylhydrosiloxane (PMHS). 相似文献
17.
Sander W Hübert R Kraka E Gräfenstein J Cremer D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(24):4567-4579
The 4-oxocyclohexa-2,5-dienylidenes are an interesting class of highly electrophilic carbenes. We investigated the reactivity of the 2,3,5,6-tetrafluorinated and -tetrachlorinated derivatives 1b and 1c with small molecules under conditions of matrix isolation. The reactions with molecular oxygen and with carbon monoxide produce the expected carbonyl O-oxides and ketenes, respectively. As a result of the extreme electrophilicity of 1b and c both carbenes insert with no or very small activation barriers into H2 or the CH bonds of hydrocarbons. Obviously, spin restrictions for these formally spin-forbidden reactions do not result in substantial thermal activation barriers. 相似文献
18.
D Schmidt JH Berthel S Pietsch U Radius 《Angewandte Chemie (International ed. in English)》2012,51(35):8881-8885
Ring expansion of NHCs! The reaction of N-heterocyclic carbenes (NHCs) with hydrosilanes Ph(4-n) SiH(n) (n=1, 2, 3) results in complete rupture of the heterocycle and silylene insertion into one of the C?N bonds of the carbene (see scheme; R=alkyl, aryl). 相似文献
19.
《Angewandte Chemie (International ed. in English)》2017,56(34):10046-10068
Discovered in 2005, cyclic (alkyl)(amino)carbenes (CAACs) are among the most nucleophilic (σ donating) and also electrophilic (π‐accepting) stable carbenes known to date. These properties allow them to activate a variety of small molecules and enthalpically strong bonds, to stabilize highly reactive main‐group and transition‐metal diamagnetic and paramagnetic species, and to bind strongly to metal centers, which gives rise to very robust catalysts. The most important results published up to the end of 2013 are briefly summarized, while the majority of this Review focuses on findings reported within the last three years. 相似文献
20.
Dr. Yang Zheng Dr. Jingxing Jiang Yue Li Yongliang Wei Junqi Zhang Prof. Dr. Jundie Hu Prof. Dr. Zhuofeng Ke Prof. Dr. Xinfang Xu Prof. Dr. Liming Zhang 《Angewandte Chemie (International ed. in English)》2023,62(17):e202218175
An oxidative strategy is reported to access α-oxo BMIDA gold carbenes directly from BMIDA-terminated alkynes. Besides offering expedient access to seldom studied boryl metal carbenes, these BMIDA gold carbene species undergo facile insertions into methyl, methylene, methine, and benzylic C−H bonds in the absence of the Thorpe–Ingold effect. They also undergo efficient OH insertion, cyclopropanation, and F−C alkylations. This chemistry provides rapid access to structurally diverse α-BMIDA ketones, which are scarcely documented. In combination with DFT studies, the role of BMIDA is established to be an electron-donating group that attenuates the high electrophilicity of the gold carbene center. 相似文献