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排序方式: 共有190条查询结果,搜索用时 31 毫秒
111.
Dr. Patrick M. Jüstel Alexandra Stan Cedric D. Pignot Dr. Armin R. Ofial 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(64):15928-15935
The kinetics of the ring-opening reactions of thiophenolates with geminal bis(acceptor)-substituted cyclopropanes in DMSO at 20 °C was monitored by photometric methods. The determined second-order rate constants of the SN2 reactions followed linear relationships with Mayr nucleophilicity parameters (N/sN) and Brønsted basicities (pKaH) of the thiophenolates as well as with Hammett substituent parameters (σ) for groups attached to the thiophenolates. Phenyl-substituted cyclopropanes reacted by up to a factor of 15 faster than their unsubstituted analogues, in accord with the known activating effect of adjacent π-systems in SN2 reactions. Variation of the electronic properties of substituents at the phenyl groups of the cyclopropanes gave rise to parabolic Hammett relationships. Thus, the inherent SN2 reactivity of electrophilic cyclopropanes is activated by electron-rich π-systems because of the more advanced C1−C2 bond polarization in the transition state. On the other hand, electron-poor π-systems also lower the energetic barriers for the attack of anionic nucleophiles owing to attractive electrostatic interactions. 相似文献
112.
Pd‐Catalyzed Regioselective Activation of gem‐Difluorinated Cyclopropanes: A Highly Efficient Approach to 2‐Fluorinated Allylic Scaffolds
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Jun Xu Ebrahim‐Alkhalil Ahmed Bin Xiao Qian‐Qian Lu Yun‐Long Wang Chu‐Guo Yu Prof. Yao Fu 《Angewandte Chemie (International ed. in English)》2015,54(28):8231-8235
An unprecedented Pd‐catalyzed regioselective activation of gem‐difluorinated cyclopropanes induced by C? C bond cleavage is reported. It provides a general and efficient access to a variety of 2‐fluoroallylic amines, ethers, esters, and alkylation products in high Z‐selectivity, which are important skeletons in many biologically active molecules. In addition, the transformation represents the first general application of gem‐difluorinated cyclopropanes as reaction partners in transition‐metal‐catalyzed cross‐coupling reaction. 相似文献
113.
114.
The (19)F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin-spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. 相似文献
115.
E. V. Trofimova A. N. Fedotov S. S. Mochalov Yu. S. Shabarov N. S. Zefirov 《Chemistry of Heterocyclic Compounds》2000,36(10):1198-1205
The acid-catalyzed conversions of N-(4-nitrobenzylidene)-2-cyclopropyl- and N-(4-nitrobenzylidene)-2-alkenylanilines have been studied. It has been established that the protonated azomethine unit of N-(4-nitrobenzylidene)-2-cyclopropylanilines is not capable of initiating intramolecular heterocyclization with participation of the three-membered ring. Conversion of N-(4-nitrobenzylidene)-2-(1-methylcyclopropyl)aniline to derivatives of quinoline is possible under the influence of concentrated H2SO4. Under the same conditions 2-methylcyclopropyl- and cyclopropyl-substituted Schiff's bases form only the corresponding alkenylazomethines (isomerization of the three-membered ring). Under the influence of more moderate acids (trifluoroacetic, polyphosphoric) N-(4-nitrobenzylidene)-2-propenyl- and N-(4-nitrobenzylidene)-2-buten-2-yl)anilines are converted to the corresponding dihydroquinolines and quinolines in high yields. N-(4-Nitrobenzylide! ne)- 2-(2,2-dimethylvinyl)aniline does not form derivatives of quinoline under the influence of the same acids in the given conditions. 相似文献
116.
Davide Moi Maria Chiara Cabua Viktoria Velichko Andrea Cocco Annalisa Chiappone Rita Mocci Stefania Porcu Monica Piras Stefano Bianco Fabio Pesciaioli Francesco Secci 《Molecules (Basel, Switzerland)》2022,27(22)
The straightforward, continuous-flow synthesis of cyclopropyl carbaldehydes and ketones has been developed starting from 2-hydroxycyclobutanones and aryl thiols. This acid-catalyzed mediated procedure allows access to the multigram and easily scalable synthesis of cyclopropyl adducts under mild conditions, using reusable Amberlyst-35 as a catalyst. The resins, suitably ground and used for filling steel columns, have been characterized via TGA, ATR, SEM and BET analyses to describe the physical–chemical properties of the packed bed and the continuous-flow system in detail. To highlight the synthetic versatility of the arylthiocyclopropyl carbonyl compounds, a series of selective oxidation reactions have been performed to access sulfoxide and sulfone carbaldehyde cyclopropanes, oxiranes and carboxylic acid derivatives. 相似文献
117.
Hillary Straub Pavel Ryabchuk Marina Rubina Michael Rubin 《Molecules (Basel, Switzerland)》2022,27(20)
Enantiomerically enriched cyclopropyl ethers, amines, and cyclopropylazole derivatives possessing three stereogenic carbon atoms in a small cycle are obtained via the diastereoselective, formal nucleophilic substitution of chiral, non-racemic bromocyclopropanes. The key feature of this methodology is the utilization of the chiral center of the cyclopropene intermediate, which governs the configuration of the two adjacent stereocenters that are successively installed via 1,4-addition/epimerization sequence. 相似文献
118.
Liu-Zhu Yu Prof. Dr. Min Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(32):7591-7606
As a special family of cyclopropanes, alkylidenecyclopropanes (ACPs), exhibit outstanding physical and chemical activities, which provide opportunities to participate in fascinating chemical transformations to access cyclopropane-containing units without ring-opening processes and other unavailable compounds through conventional routes with ring-opening processes owing to their strain-driven reactivity and synthetic accessibility. Nowadays, intramolecular reactions of methylenecyclopropanes (MCPs) or ACPs with adjacent functionalities have emerged as a powerful synthetic protocol for the construction of a variety of polycyclic and heterocyclic compounds with different sized skeletons through catalytic methods. Recently, we put forward the concept of functional alkylidenecyclopropanes (FACPs) and in this Minireview, we will summarize the reactions of FACPs after 2016 including several important early works from three aspects: 1) reactions with distal C−C bond cleavage, 2) reactions with proximal C−C bond cleavage (including ring-expansion reactions), and 3) reactions without C−C bond cleavage. 相似文献
119.
《Mendeleev Communications》2021,31(5):654-656
New N-Boc-alkyl(2-alkynylcyclopropyl)amines were synthesized from 1-alkynyl-1-chlorocyclopropanes and N-Boc- alkylamines under the action of ButOK in DMSO, the intermediates having been the corresponding conjugated alkynylcyclopropenes. The Boc-derivatives can be converted into free secondary 2-alkynylcyclopropylamines, as well as β-lithiated with subsequent alkylation. 相似文献
120.
Hui Wang Ren-Yin Yang Dr. Bo Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(23):e202104364
A facile synthesis of cyclopropenes and fluorinated cyclopropanes from readily available alkyl triflones was developed. The reaction, regardless of electronic effect, gave products in good to excellent yields and moderate diastereoselectivity. The mechanism may involve tandem Michael addition of triflones/intramolecular nucleophilic cyclization (elimination of -SO2CF3)/elimination of fluoride. 相似文献