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1.
The reaction of dilithium biphenyl (Li2C12H10) with alkyl fluorides has been studied from the point of view of the distribution of products. Two main reaction pathways, the nucleophilic substitution (SN2) and the electron transfer (ET), can compete to yield the same alkylation products in what is known as the SN2-ET dichotomy. SN2 seems to be the main mechanism operating with primary alkyl fluorides (n-RF). Alkylation proceeds in good yields, and the resulting alkylated dihydrobiphenyl anion (n-RC12H10Li) can be trapped with a second conventional electrophile (E+) affording synthetically interesting dearomatized biphenyl derivatives (n-RC12H10E). The reaction gives a higher amount of ET products as we move to secondary (s-RF) and to tertiary alkyl fluorides (t-RF), in which case the mechanism seems to be dominated by ET. In this case, alkylation by radical coupling is still feasible, giving access to the synthesis of t-RC12H10E, although in lower yields. A rational interpretation of this SN2-ET dichotomy is given on the basis of the full distribution of products observed when 5-hexenyl fluoride and 1,1-dimethyl-5-hexenyl fluoride were are used as radical probes in their reaction with Li2C12H10 and LiC12H10. 相似文献
2.
Visible‐Light‐Promoted Photocatalytic B−C Coupling via a Boron‐Centered Carboranyl Radical: Facile Synthesis of B(3)‐Arylated o‐Carboranes
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Dr. Da Zhao Prof. Dr. Zuowei Xie 《Angewandte Chemie (International ed. in English)》2016,55(9):3166-3170
A visible‐light‐mediated in situ generation of a boron‐centered carboranyl radical (o‐C2B10H11 . ) has been described. With eosin Y as a photoredox catalyst, 3‐diazonium‐o‐carborane tetrafluoroborate [3‐N2‐o‐C2B10H11][BF4] was converted into the corresponding boron‐centered carboranyl radical intermediate, which can undergo efficient electrophilic substitution reaction with a wide range of (hetero)arenes. This general and simple procedure provides a metal‐free alternative for the synthesis of 3‐(hetero)arylated‐o‐carboranes. 相似文献
3.
Daniele Ciceri AntonioJ. Pierik Günter Hartrampf Gerd Brker Giovanna Speranza Wolfgang Buckel SirJohn Cornforth BernardT. Golding 《Helvetica chimica acta》2000,83(9):2550-2561
2‐Methylideneglutarate mutase is an adenosylcobalamin (coenzyme B12)‐dependent enzyme that catalyses the equilibration of 2‐methylideneglutarate with (R)‐3‐methylitaconate. This reaction is believed to occur via protein‐bound free radicals derived from substrate and product. The stereochemistry of the formation of the methyl group of 3‐methylitaconate has been probed using a `chiral methyl group'. The methyl group in 3‐([2H1,3H]methyl)itaconate derived from either (R)‐ or (S)‐2‐methylidene[3‐2H1,3‐3H1]glutarate was a 50 : 50 mixture of (R)‐ and (S)‐forms. It is concluded that the barrier to rotation about the C−C bond between the methylene radical centre and adjacent C‐atom in the product‐related radical [.CH2CH(−O2CC=CH2)CO2−] is relatively low, and that the interaction of the radical with cob(II)alamin is minimal. Hence, cob(II)alamin is a spectator of the molecular rearrangement of the substrate radical to product radical. 相似文献
4.
Julien Coulomb Victor Certal Dr. Marie‐Hélène Larraufie Cyril Ollivier Dr. Jean‐Pierre Corbet Dr. Gérard Mignani Dr. Louis Fensterbank Prof. Emmanuel Lacôte Dr. Max Malacria Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10225-10232
A general and efficient method for the synthesis of cyclic sulfinates and sulfinamides based on intramolecular homolytic substitution (SHi) at the sulfur atom by aryl or alkyl radicals is described. Both alkyl and benzofused compounds can be accessed directly from easily prepared acyclic precursors. Enantiomerically enriched sulfur‐based heterocycles were formed through an SHi process with inversion of configuration at the sulfur atom. Cyclization of prochiral radicals proceeded with varying stereochemical outcomes, depending on the size of the incoming radical. 2‐Pyridyl and 2‐quinolyl radicals led to biaryl compounds, which result from attack onto the ortho position of the arylsulfinate rather than a thiophilic substitution. 相似文献
5.
Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas‐Phase Reactions of Alkyl Radicals with NF3
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Dr. Paola Antoniotti Dr. Paola Benzi Dr. Stefano Borocci Dr. Chiara Demaria Dr. Maria Giordani Prof. Felice Grandinetti Prof. Lorenza Operti Prof. Roberto Rabezzana 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15826-15834
The X‐ray irradiation of binary mixtures of alkyl iodides R?I (R=CH3, C2H5, or i‐C3H7 radicals) and NF3 produces R?NF2 and R?F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (SH2) by the alkyl radicals R, which attack the N atom of NF3. This mechanism is consistent with the suppression of R?NF2 by addition of O2 (an efficient alkyl radical scavenger) to the reaction mixture. The R?F product arises from the attack of R to the F atom of NF3, but additional contributing channels are conceivably involved. The F‐atom abstraction is, indeed, considerably more exothermic than the SH2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast. 相似文献
6.
The structure of t-Bu3Si?H2, (I), suggested that it might be a persistent primary alkyl radical since it has (i) a bulky group to protect the radical center; (ii) no β-hydrogens, so that a radical-radical disproportionation reaction is impossible; (iii) a β-silicon atom, which should prevent β-scission of tert-butyl as a unimolecular decomposition pathway. However, the self-reaction of (I) in isooctane was found to be a diffusion controlled process with log(A/M?1 sec?1) = 10.7 ± 0.3 and E = 2.5 ± 0.2 kcal mole?1. Hence (I) is not persistent and it is concluded that a persistent primary alkyl will only be observed when the—?H2 moiety is deeply buried among sterically protecting groups. 相似文献
7.
Robert A. Batey David V. Smil 《Angewandte Chemie (International ed. in English)》1999,38(12):1798-1800
5-, 6-, and even 7- exo -trig radical cyclizations ( 1 → 2 ) are possible by applying a new boron-tethering approach with alkenylboronic esters. For certain substitution patterns, a subsequent intramolecular homolytic substitution (SHi) reaction at boron occurs ( 2 → 3 ) and leads to rearranged products. The C−B bond of the intermediate boracycles is readily oxidized to give diol products. 相似文献
8.
Biotransformation of (±)‐threo‐7,8‐dihydroxy(7,8‐2H2)tetradecanoic acids (threo‐(7,8‐2H2)‐ 3 ) in Saccharomyces cerevisiae afforded 5,6‐dihydroxy(5,6‐2H2)dodecanoic acids (threo‐(5,6‐2H2)‐ 4 ), which were converted to (5S,6S)‐6‐hydroxy(5,6‐2H2)dodecano‐5‐lactone ((5S,6S)‐(5,6‐2H2)‐ 7 ) with 80% e.e. and (5S,6S)‐5‐hydroxy(5,6‐2H2)dodecano‐6‐lactone ((5S,6S)‐5,6‐2H2)‐ 8 ). Further β‐oxidation of threo‐(5,6‐2H2)‐ 4 yielded 3,4‐dihydroxy(3,4‐2H2)decanoic acids (threo‐(3,4‐2H2)‐ 5 ), which were converted to (3R,4R)‐3‐hydroxy(3,4‐2H2)decano‐4‐lactone ((3R,4R)‐ 9 ) with 44% e.e. and converted to 2H‐labeled decano‐4‐lactones ((4R)‐(3‐2H1)‐ and (4R)‐(2,3‐2H2)‐ 6 ) with 96% e.e. These results were confirmed by experiments in which (±)‐threo‐3,4‐dihydroxy(3,4‐2H2)decanoic acids (threo‐(3,4‐2H2)‐ 5 ) were incubated with yeast. From incubations of methyl (5S,6S)‐ and (5R,6R)‐5,6‐dihydroxy(5,6‐2H2)dodecanoates ((5S,6S)‐ and (5R,6R)‐(5,6‐2H2)‐ 4a ), the (5S,6S)‐enantiomer was identified as the precursor of (4R)‐(3‐2H1)‐ and (2,3‐2H2)‐ 6 ). Therefore, (4R)‐ 6 is synthesized from (3S,4S)‐ 5 by an oxidation/keto acid reduction pathway involving hydrogen transfer from C(4) to C(2). In an analogous experiment, methyl (9S,10S)‐9,10‐dihydroxyoctadecanoate ((9S,10S)‐ 10a ) was metabolized to (3S,4S)‐3,4‐dihydroxydodecanoic acid ((3S,4S)‐ 15 ) and converted to (4R)‐dodecano‐4‐lactone ((4R)‐ 18 ). 相似文献
9.
Dilithium naphthalene (Li2C10H8) displays a SN2 reactivity profile in its reaction with alkyl fluorides (n-, s- and t-octyl fluoride). SN2 seems to be the dominant mechanism operating with primary alkyl fluorides, which presumably turns into competition with ET as we move to secondary and tertiary alkyl fluorides. Significantly, lithium naphthalene (LiC10H8) seems to have also an important nucleophilic component when reacting with alkyl fluorides, in contrast to the previously proposed general ET process valid for all alkyl halides. These results explain the observed distribution of products and are reinforced by a complete analysis of the products originated by the reaction with 6-halohexenyl radical probes, whose main alkylation products are described here for the first time. 相似文献
10.
Linjun Qi Ming Dong Jinlong Qian Shuling Yu Prof. Xiaofeng Tong 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202215397
Reductive elimination of alkyl−PdII−O is a synthetically useful yet underdeveloped elementary reaction. Here we report that the combination of an H-bonding donor [PyH][BF4] and AgNO3 additive under toluene/H2O biphasic system can enable such elementary step to form alkyl nitrate. This results in the Pd0-catalyzed asymmetric carbonitratations of (Z)-1-iodo-1,6-dienes with (R)-BINAP as the chiral ligand, affording alkyl nitrates up to 96 % ee. Mechanistic studies disclose that the reaction consists of oxidative addition of Pd0 catalyst to vinyl iodide, anion ligand exchange between I− and NO3−, alkene insertion and SN2-type alkyl−PdII−ONO2 reductive elimination. Evidences suggest that H-bonding interaction of PyH⋅⋅⋅ONO2 can facilitate dissociation of O2NO− ligand from the alkyl−PdII−ONO2 species, thus enabling the challenging alkyl−PdII−ONO2 reductive elimination to be feasible. 相似文献
11.
Peng Zhou Wei Ren Gang Nie Xiaojie Li Dr. Xiaoguang Duan Yongli Zhang Prof. Shaobin Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16660-16669
Generation of hydroxyl radicals in the Fenton system (FeII/H2O2) is seriously limited by the sluggish kinetics of FeIII reduction and fast FeIII precipitation. Here, boron crystals (C-Boron) remarkably accelerate the FeIII/FeII circulation in Fenton-like systems (C-Boron/FeIII/H2O2) to produce a myriad of hydroxyl radicals with excellent efficiencies in oxidative degradation of various pollutants. The surface B−B bonds and interfacial suboxide boron in the surface B12 icosahedra are the active sites to donate electrons to promote fast FeIII reduction to FeII and further enhance hydroxyl radical production via Fenton chemistry. The C-Boron/FeIII/H2O2 system outperforms the benchmark Fenton (FeII/H2O2) and FeIII-based sulfate radical systems. The reactivity and stability of crystalline boron is much higher than the popular molecular reducing agents, nanocarbons, and other metal/metal-free nanomaterials. 相似文献
12.
Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex
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Lucía Piñeiro‐López Dr. Norma Ortega‐Villar Prof. Dr. M. Carmen Muñoz Dr. Gábor Molnár Dr. Jordi Cirera Prof. Dr. Rafael Moreno‐Esparza Prof. Dr. Víctor M. Ugalde‐Saldívar Dr. Azzedine Bousseksou Prof. Dr. Eliseo Ruiz Prof. Dr. José A. Real 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12741-12751
The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6)2 (bztpen=N‐benzyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethylenediamine) displays an S=1/2?S=3/2 spin crossover (SCO) behavior (T1/2=370 K, ΔH=12.48 kJ mol?1, ΔS=33 J K?1 mol?1) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0?S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120–420 K affording a detailed picture of how the electronic distribution of the t2g–eg orbitals modulates the structure of the {FeNO}7 bond, providing valuable magneto–structural and spectroscopic correlations and DFT analysis. 相似文献
13.
Dr. Olivier Berger Prof. Jean‐Luc Montchamp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12385-12388
The intermolecular radical functionalization of arenes with aryl and alkyl H‐phosphinate esters, as well as diphenylphosphine oxide and H‐phosphonate diesters, is described. The novel catalytic MnII/excess MnIV system is a convenient and inexpensive solution to directly convert Csp2?H into C?P bonds. The reaction can be employed to functionalize P‐stereogenic H‐phosphinates since it is stereospecific. With monosubstituted aromatics, the selectivity for para‐substitution increases in the order (RO)2P(O)H<R1P(O)(OR)H<Ph2P(O)H, a trend that may be explained by steric effects. 相似文献
14.
The radical copolymerization of dialkyl citraconate (DRC, R[dbnd]CH3, C2H5, n-C3H7, i-C3H7, n-C4H9, i-C4H9, s-C4H9, C6H11, C6H5CH2) (M1) with styrene (ST, M2) was performed at 60°C, using azobisisobutyronitrile as the initiator in tetrahydrofuran in order to clarify the polymerization behavior of DRC and the substituent effects on copolymerization. The monomer reactivity ratios r1 and r2 and the Q1 and e1 values were determined from the results obtained. It was found that the relative reactivities 1/r2 of DRC toward an attack by a polystyryl radical could be correlated not by the steric-substituent constant ES of the alkyl group in DRC, but by the polar-substituent constants σ? in Taft' equation: log (1/r2) = ρσ + δES. It was also observed that the e1 values are associated with Taft' σ constant. It was found that the weight-average molecular weights of the copolymers are between 8.5 × 103 and 1.4 × 104. 相似文献
15.
Edison Osorio Dr. Jared K. Olson Prof. William Tiznado Prof. Alexander I. Boldyrev 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(31):9677-9681
We performed global minimum searches for the BnHn+2 (n=2‐5) series and found that classical structures composed of 2c–2e B? H and B? B bonds become progressively less stable along the series. Relative energies increase from 2.9 kcal mol?1 in B2H4 to 62.3 kcal mol?1 in B5H7. We believe this occurs because boron atoms in the studied molecules are trying to avoid sp2 hybridization and trigonal structure at the boron atoms, as in that case one 2p‐AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p‐AOs and avoiding having one 2p‐AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron–hydride clusters as well as for pure boron clusters and boron compounds in general. 相似文献
16.
Hong Yi Wenbin Mao Martin Oestreich 《Angewandte Chemie (International ed. in English)》2019,58(11):3575-3578
An enantioselective C(sp3)?C(sp3) cross‐coupling of racemic α‐silylated alkyl iodides and alkylzinc reagents is reported. The reaction is catalyzed by NiCl2/(S,S)‐Bn‐Pybox and yields α‐chiral silanes with high enantiocontrol. The catalyst system does not promote the cross‐coupling of the corresponding carbon analogue, corroborating the stabilizing effect of the silyl group on the alkyl radical intermediate (α‐silicon effect). Both coupling partners can be, but do not need to be, functionalized, and hence, even α‐chiral silanes with no functional group in direct proximity of the asymmetrically substituted carbon atom become accessible. This distinguishes the new method from established approaches for the synthesis of α‐chiral silanes. 相似文献
17.
The rate coefficients for the gas-phase reactions of C2H5O2 and n-C3H7O2 radicals with NO have been measured over the temperature range of (201–403) K using chemical ionization mass spectrometric detection of the peroxy radical. The alkyl peroxy radicals were generated by reacting alkyl radicals with O2, where the alkyl radicals were produced through the pyrolysis of a larger alkyl nitrite. In some cases C2H5 radicals were generated through the dissociation of iodoethane in a low-power radio frequency discharge. The discharge source was also tested for the i-C3H7O2 + NO reaction, yielding k298 K = (9.1 ± 1.5) × 10−12 cm3 molecule−1 s−1, in excellent agreement with our previous determination. The temperature dependent rate coefficients were found to be k(T) = (2.6 ± 0.4) × 10−12 exp{(380 ± 70)/T} cm3 molecule−1 s−1 and k(T) = (2.9 ± 0.5) × 10−12 exp{(350 ± 60)/T} cm3 molecule−1 s−1 for the reactions of C2H5O2 and n-C3H7O2 radicals with NO, respectively. The rate coefficients at 298 K derived from these Arrhenius expressions are k = (9.3 ± 1.6) × 10−12 cm3 molecule−1 s−1 for C2H5O2 radicals and k = (9.4 ± 1.6) × 10−12 cm3 molecule−1 s−1 for n-C3H7O2 radicals. © 1996 John Wiley & Sons, Inc. 相似文献
18.
Mariana Dennehy Oscar V. Quinzani Ricardo Faccio Eleonora Freire lvaro W. Mombrú 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(1):m12-m16
(Acetonitrile‐1κN)[μ‐1H‐benzimidazole‐2(3H)‐thione‐1:2κ2S:S][1H‐benzimidazole‐2(3H)‐thione‐2κS]bis(μ‐1,1‐dioxo‐1λ6,2‐benzothiazole‐3‐thiolato)‐1:2κ2S3:N;1:2κ2S3:S3‐dicopper(I)(Cu—Cu), [Cu2(C7H4NO2S2)2(C7H6N2S)2(CH3CN)] or [Cu2(tsac)2(Sbim)2(CH3CN)] [tsac is thiosaccharinate and Sbim is 1H‐benzimidazole‐2(3H)‐thione], (I), is a new copper(I) compound that consists of a triply bridged dinuclear Cu—Cu unit. In the complex molecule, two tsac anions and one neutral Sbim ligand bind the metals. One anion bridges via the endocyclic N and exocyclic S atoms (μ‐S:N). The other anion and one of the mercaptobenzimidazole molecules bridge the metals through their exocyclic S atoms (μ‐S:S). The second Sbim ligand coordinates in a monodentate fashion (κS) to one Cu atom, while an acetonitrile molecule coordinates to the other Cu atom. The CuI—CuI distance [2.6286 (6) Å] can be considered a strong `cuprophilic' interaction. In the case of [μ‐1H‐benzimidazole‐2(3H)‐thione‐1:2κ2S:S]bis[1H‐benzimidazole‐2(3H)‐thione]‐1κS;2κS‐bis(μ‐1,1‐dioxo‐1λ6,2‐benzothiazole‐3‐thiolato)‐1:2κ2S3:N;1:2κ2S3:S3‐dicopper(I)(Cu—Cu), [Cu2(C7H4NO2S2)2(C7H6N2S)3] or [Cu2(tsac)2(Sbim)3], (II), the acetonitrile molecule is substituted by an additional Sbim ligand, which binds one Cu atom via the exocylic S atom. In this case, the CuI—CuI distance is 2.6068 (11) Å. 相似文献
19.
Peng Zhou Wei Ren Gang Nie Xiaojie Li Xiaoguang Duan Yongli Zhang Shaobin Wang 《Angewandte Chemie (International ed. in English)》2020,59(38):16517-16526
Generation of hydroxyl radicals in the Fenton system (FeII/H2O2) is seriously limited by the sluggish kinetics of FeIII reduction and fast FeIII precipitation. Here, boron crystals (C‐Boron) remarkably accelerate the FeIII/FeII circulation in Fenton‐like systems (C‐Boron/FeIII/H2O2) to produce a myriad of hydroxyl radicals with excellent efficiencies in oxidative degradation of various pollutants. The surface B?B bonds and interfacial suboxide boron in the surface B12 icosahedra are the active sites to donate electrons to promote fast FeIII reduction to FeII and further enhance hydroxyl radical production via Fenton chemistry. The C‐Boron/FeIII/H2O2 system outperforms the benchmark Fenton (FeII/H2O2) and FeIII‐based sulfate radical systems. The reactivity and stability of crystalline boron is much higher than the popular molecular reducing agents, nanocarbons, and other metal/metal‐free nanomaterials. 相似文献
20.
Gupta Krishna S. Bhargava Pinky Manoj Sreedharan V. Bhargava Rachna 《Transition Metal Chemistry》2000,25(3):329-332
The kinetics of the silver(I) catalysed autoxidation of aqueous sulphur(IV) an acetate buffered medium obey the rate law: –d[SIV]/dt = D[AgI][SIV]2[H+]–1/(B+C[SIV]). The rate is independent of [O2] but strongly inhibited by EtOH. A free radical mechanism is proposed. 相似文献