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Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.


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Journal ArticleDOI
TL;DR: Air-stable and commercially available alkynophilic metal salts, such as PtCl2, PtCl4, and [RuCl2(CO)3]2, catalyze the cycloisomerization of 1-alkyl-2-ethynylbenzenes to produce substituted indenes even at an ambient temperature.
Abstract: Air-stable and commercially available alkynophilic metal salts, such as PtCl2, PtCl4, and [RuCl2(CO)3]2, catalyze the cycloisomerization of 1-alkyl-2-ethynylbenzenes to produce substituted indenes even at an ambient temperature. Electrophilically activated alkynes can be intercepted by simple benzylic C−H bonds at primary, secondary, and tertiary carbon centers. Mechanistic studies, such as labeling studies and kinetic isotope and substituent effects, indicate that the cycloisomerization proceeds through the formation of a vinylidene intermediate and turnover-limiting 1,5-shift of benzylic hydrogen.

104 citations

Journal ArticleDOI
TL;DR: This study represents the synthesis of a new series of N-substituted phenyl-5-methyl-6-(5-(4- substituting phenyl)-1,3,4-oxadiazol-2-yl)thieno[2,3-d]pyrimidin-4-amine derivatives and substituted phenylamino- 5-methylthienospyrimidine-6-carboxylic acid derivatives.

104 citations

Journal ArticleDOI
TL;DR: A new class of chiral phosphines belonging to the P-aryl-2-phosphabicyclo[3.3.0]octane family (PBO) has been prepared by enantioselective synthesis starting from lactate esters and 2,2-dimethylcyclopentanone enolate 5.
Abstract: A new class of chiral phosphines belonging to the P-aryl-2-phosphabicyclo[3.3.0]octane family (PBO) has been prepared by enantioselective synthesis starting from lactate esters and 2,2-dimethylcyclopentanone enolate 5. A selective enolate alkylation method has been developed for preparation of 9 and 10 using a chelating ester substituent in the triflate alkylating agent 11. Subsequent conversion to the PBO catalysts 2 and 39 relies on a diastereoselective cyclization from the cyclic sulfate 17 and LiPHAr to afford the more hindered endo-aryl phosphines. These phosphines function as efficient catalysts for the kinetic resolutions of aryl alkyl carbinols by benzoylation (16, 21, 22) or iso-butyroylation in the case of the less hindered aryl alkyl carbinol substrates. With o-substituted aryl alkyl carbinols, the enantioselectivities exceed 100, and s = 380 ± 10 has been demonstrated in the case of methyl mesityl carbinol. The PBO-catalyzed acylations probably involve a P-acylphosphonium carboxylate intermedi...

104 citations

Journal ArticleDOI
TL;DR: The ratio of binding affinities for the two compounds is smaller than the true contribution of the hydroxyl group, a conclusion with significant bearing on interpreting difference free energies derived from substituent effects arising from chemical modification and/or mutagenesis.
Abstract: Cytidine deaminase binds transition-state analog inhibitors approximately 10(7) times more tightly than corresponding 3,4-dihydro analogs containing a proton in place of the 4-hydroxyl group. X-ray crystal structures of complexes with the two matched inhibitors differ only near a "trapped" water molecule in the complex with the 3,4-dihydro analog, where contacts are substantially less favorable than those with the hydroxyl group of the transition-state analog. The hydrogen bond between the hydroxyl group and the Glu 104 carboxylate shortens in that complex, and may become a "low-barrier" hydrogen bond, since at the same time the bond between zinc and the Cys 132 thiolate ligand lengthens. These differences must therefore account for most of the differential binding affinity related to catalysis. Moreover, the trapped water molecule retains some of the binding energy stabilizing the hydroxyl group in the transition-state analog complex. To this extent, the ratio of binding affinities for the two compounds is smaller than the true contribution of the hydroxyl group, a conclusion with significant bearing on interpreting difference free energies derived from substituent effects arising from chemical modification and/or mutagenesis.

104 citations

Journal ArticleDOI
TL;DR: The bond dissociation energies of the benzylic C-H bond of a series of 16 para-substituted toluene compounds (p-X-C(6)H(4)CH(3)) have been calculated with the density functional method (BLYP/6-31G).
Abstract: The bond dissociation energies of the benzylic C-H bond of a series of 16 para-substituted toluene compounds (p-X-C(6)H(4)CH(3)) have been calculated with the density functional method (BLYP/6-31G). The calculated substituent effects correlate well with experimental rates of dimerization of para-substituted alpha,beta,beta-trifluorostyrenes and rearrangement of methylenearylcyclopropanes. Both electron-donating and electron-withdrawing groups reduce the bond dissociation energy (BDE) of the benzylic C-H bond because both groups cause spin delocalization from the benzylic radical center. The calculated spin density variations at the benzylic radical centers correlate well with both the ESR hyperfine coupling constants determined by Arnold et al. and the calculated radical effects of the substituents. The relative radical stabilities are mainly determined by the spin delocalization effect of the substituents, and polar effect of the substituents are not important in the current situation. The ground state effect is also found to influence the C-H BDE.

104 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023660
20221,273
2021568
2020787
2019753
2018858