- Insights into the asymmetric heterogeneous catalysis in porous organic polymers: Constructing A TADDOL-Embedded chiral catalyst for studying the structure-activity relationship[ ]
-
Construction of porous organic polymers (POPs) as asymmetric catalysts remains as an important but challenging task. Herein, we exploit the "bottom-up" strategy to facilely synthesize an α,α, α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-based chiral porous polymer (TADDOL-CPP) for highly efficient asymmetric catalysis. Constructed through the covalent linkages among the three-dimensional rigid monomers, TADDOL-CPP possesses hierarchical porous structure, high Brunauer-Emmett-Teller (BET) surface area, together with abundant and uniformly-distributed chiral sites. In the presence of [Ti(OiPr)4], TADDOL-CPP acts as a highly efficient and recyclable catalyst in the asymmetric addition of diethylzinc (Et2Zn) to aromatic aldehydes. Based on the direct observation of the key intermediates, the reaction mechanism has been revealed by solid-state 13C magic-angle spinning (MAS) NMR spectroscopy. In combination with the catalytic testing results, characterization on the working catalyst provides further information for understanding the structure-activity relationship. We suggest that the catalytic activity of TADDOL-CPP is largely affected by the structural rigidity, cooperative catalysis, local chiral environment, and hierarchical porous framework. We expect that the information obtained herein will benefit to the designed synthesis of robust POP catalysts toward practical applications.
- An, Wan-Kai,Han, Man-Yi,Wang, Chang-An,Yu, Si-Min,Zhang, Yuan,Bai, Shi,Wang, Wei
-
p. 11019 - 11028,10
(2014)
-
Read Online
- On the mechanism of addition of lithium pinacolone enolate to benzaldehyde: Polar or electron transfer?
-
The carbonyl-carbon kinetic isotope effect (KIE) and the substituent effect were measured for the reaction of lithium pinacolone enolate (CH2=C(OLi)C(CH3)3) with benzaldehyde, and the results were compared with those for other lithium reagents such as MeLi, PhLi, and CH2=CHCH2Li. Ab initio MO calculations (HF/6-31+G*) were carried out to estimate the equilibrium IE on the addition to benzaldehyde. A carbonyl addition reaction, in general, proceeds by way of either a polar direct nucleophilic attack (PL) in a one-step or a two-step process going through a radical ion intermediate (eq 1). The carbonyl-carbon KIE is of primary nature for the PL or the RC rate-determining ET mechanism, while it is considered to be secondary for the ET rate-determining mechanism. The reaction of lithium pinacolone enolate with benzaldehyde gave a small positive KIE (12k/13k = 1.019), which is larger than the theoretical equilibrium IE (12K/13K = 1.006) determined by the MO calculations. Thus, there is a reaction-coordinate contribution to the observed KIE. This is in sharp contrast to the absence of KIE (12k/14k = 1.000) measured previously for the MeLi addition. Dehalogenation and enone-isomerization probe experiments showed no evidence of a single electron transfer to occur during the course of the reaction. The primary carbonyl-carbon KIE together with the substituent effect and chemical probe experiments led to the conclusion that the reaction of lithium pinacolone enolate with benzaldehyde proceeds via the polar mechanism.
- Yamataka, Hiroshi,Sasaki, Daizo,Kuwatani, Yoshiyuki,Mishima, Masaaki,Tsuno, Yuho
-
-
Read Online
- Reaction of magnesium pinacolone enolate with benzaldehyde: Polar or ET mechanism?
-
The carbonyl-carbon kinetic isotope effect (KIE) and the substituent effect were measured for the reaction of magnesium pinacolone enolate (CH2=C(OMgBr)C(CH3)3, 1) with benzaldehyde. The results were compared with those for lithium enolate (CH2=C(OLi)C(CH3)3, 2). A normal carbonyl-carbon KIE, a medium-sized Hammett ρ value and the results of chemical probe experiments indicated that the reaction of 1 proceeds via the polar mechanism as in the reaction of 2.
- Yamataka, Hiroshi,Shimizu, Makoto,Mishima, Masaaki
-
-
Read Online
- BIOSYNTHESIS OF THE BENZOYL MOIETY OF COCAINE FROM CINNAMIC ACID VIA (R)-(+)-3-HYDROXY-3-PHENYLPROPANOIC ACID
-
trans-Cinnamic acid and the N-acetylcysteamine thioester of -trans-cinnamic acid served as precursors of the benzoyl moiety of cocaine when fed to intact Erythroxylum coca plants.The specific incorporation of the thioester in
- Bjorklund, Jeffrey A.,Leete, Edward
-
-
Read Online
- Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas
-
The reductive carbonylation of aryl iodides to aryl aldehydes possesses broad application prospects. We present an efficient and facile Rh-based catalytic system composed of the commercially available Rh salt RhCl3·3H2O, PPh3 as phosphine ligand, and Et3N as the base, for the synthesis of arylaldehydes via the reductive carbonylation of aryl iodides with CO and H2 under relatively mild conditions with a broad substrate range affording the products in good to excellent yields. Systematic investigations were carried out to study the experimental parameters. We explored the optimal ratio of Rh salt and PPh3 ligand, substrate scope, carbonyl source and hydrogen source, and the reaction mechanism. Particularly, a scaled-up experiment indicated that the catalytic method could find valuable applications in industrial productions. The low gas pressure, cheap ligand and low metal dosage could significantly improve the practicability in both chemical researches and industrial applications.
- Chen, Suqing,Liu, Zhenghui,Mu, Tiancheng,Wang, Peng,Yan, Zhenzhong,Yu, Dongkun,Zhao, Xinhui
-
p. 645 - 656
(2020/05/14)
-
- Catalytic Enantioselective [2,3]-Rearrangements of Allylic Ammonium Ylides: A Mechanistic and Computational Study
-
A mechanistic study of the isothiourea-catalyzed enantioselective [2,3]-rearrangement of allylic ammonium ylides is described. Reaction kinetic analyses using 19F NMR and density functional theory computations have elucidated a reaction profile
- West, Thomas H.,Walden, Daniel M.,Taylor, James E.,Brueckner, Alexander C.,Johnston, Ryne C.,Cheong, Paul Ha-Yeon,Lloyd-Jones, Guy C.,Smith, Andrew D.
-
supporting information
p. 4366 - 4375
(2017/04/04)
-
- Metathesis Reaction of Diazo Compounds and para-Quinone Methides for C-C Double Bond Formation: Synthesis of Tetrasubstituted Alkenes and Quinolinones
-
The para-quinone methides (p-QMs) are activated by Lewis acid and then attacked by diazo compounds. The following rearrangement leads to nitrogen gas extrusion and C-C double bond formation to constitute a metathesis reaction process. Therefore, the diazo
- Huang, Bo,Shen, Yangyong,Mao, Zhenjun,Liu, Yu,Cui, Sunliang
-
supporting information
p. 4888 - 4891
(2016/10/18)
-
- Asymmetric 1,2-Perfluoroalkyl Migration: Easy Access to Enantioenriched α-Hydroxy-α-perfluoroalkyl Esters
-
This study has led to the development of a novel, highly efficient, 1,2-perfluoro-alkyl/-aryl migration process in reactions of hydrate of 1-perfluoro-alkyl/-aryl-1,2-diketones with alcohols, which are promoted by a Zn(II)/bisoxazoline and form α-perfluoro-alkyl/-aryl-substituted α-hydroxy esters. With (-)-8-phenylmenthol as the alcohol, the corresponding menthol esters are generated in high yields with excellent levels of diastereoselectivity. The mechanistic studies show that the benzilic ester-type rearrangement reaction takes place via an unusual 1,2-migration of electron-deficient trifluoromethyl group rather than the phenyl group. The overall process serves as a novel, efficient, and simple approach for the synthesis of highly enantioenriched, biologically relevant α-hydroxy-α-perfluoroalkyl carboxylic acid derivatives.
- Wang, Pan,Feng, Liang-Wen,Wang, Lijia,Li, Jun-Fang,Liao, Saihu,Tang, Yong
-
p. 4626 - 4629
(2015/04/27)
-
- Gold-catalyzed 1,3-transposition of ynones
-
An efficient, regioselective gold-catalyzed 1,3-transposition reaction of ynones and diynones has been developed. It was found that stereoelectronic (interrupted conjugation) and electronic (extended conjugation) factors could efficiently govern the regio
- Kazem Shiroodi, Roohollah,Soltani, Mohammad,Gevorgyan, Vladimir
-
p. 9882 - 9885
(2014/08/05)
-
- Isotopic labelling studies for a gold-catalysed skeletal rearrangement of alkynyl aziridines
-
Isotopic labelling studies were performed to probe a proposed 1,2-aryl shift in the gold-catalysed cycloisomerisation of alkynyl aziridines into 2,4-disubstituted pyrroles. Two isotopomers of the expected skeletal rearrangement product were identified usi
- Davies, Paul W.,Martin, Nicolas,Spencer, Neil
-
supporting information; experimental part
p. 839 - 846
(2011/08/10)
-
- Imidazolium ionic liquids as solvents for cerium(IV)-mediated oxidation reactions
-
Use of imidazolium ionic liquids as solvents for organic transformations with tetravalent cerium salts as oxidizing agents was evaluated. Good solubility was found for ammonium hexanitratocerate(IV) (ceric ammonium nitrate, CAN) and cerium(IV) triflate in 1-alkyl-3-methylimidazolium triflate ionic liquids. Oxidation of benzyl alcohol to benzaldehyde in 1-ethyl-3-methylimidazolium triflate was studied by in-situ FTIR spectroscopy and 13C NMR spectroscopy on carbon-13-labeled benzyl alcohol. Careful control of the reaction conditions is necessary because ammonium hexanitratocerate(IV) dissolved in an ionic liquid can transform benzyl alcohol not only into benzaldehyde but also into benzyl nitrate or benzoic acid. The selectivity of the reaction of cerium(IV) triflate with benzyl alcohol in dry ionic liquids depends on the degree of hydration of cerium(IV) triflate: anhydrous cerium(IV) triflate transforms benzyl alcohol into dibenzyl ether, whereas hydrated cerium(IV) triflate affords benzaldehyde as the main reaction product. Reactions of ammonium hexanitratocerate(IV) with organic substrates other than benzyl alcohol have been explored. 1,4-Hydroquinone is quantitatively transformed into 1,4-quinone. Anisole and naphthalene are nitrated. For the cerium-mediated oxidation reactions in ionic liquids, high reaction temperatures are an advantage because under these conditions smaller amounts of byproducts are formed.
- Mehdi, Hasan,Bodor, Andrea,Lantos, Diana,Horvath, Istvan T.,De Vos, Dirk E.,Binnemans, Koen
-
p. 517 - 524
(2007/10/03)
-
- A m-benzyne to o-benzyne conversion through a 1,2-shift of a phenyl group
-
Pyrolysis of two differently labeled versions of 3-phenylphthalic anhydride shows that a m-benzyne can form the related o-benzyne through shift of a phenyl group. The highest energy point in the process is the transition structure for a reverse carbon-hyd
- Blake, Michael E.,Bartlett, Kevin L.,Jones Jr., Maitland
-
p. 6485 - 6490
(2007/10/03)
-
- Structure of the modified heme in allylbenzene-inactivated chloroperoxidase determined by Q-band CW and pulsed ENDOR
-
During the epoxidation of allylbenzene, chloroperoxidase (CPO) is converted to an inactive green species in which the prosthetic heme has been modified by addition of the alkene plus an oxygen atom (Dexter, A. F.; Hager, L. P. J. Am. Chem. Soc. 1995, 117,
- Lee, Hong-In,Dexter, Annette F.,Fann, Yang-Cheng,Lakner, Frederick J.,Hager, Lowell P.,Hoffman, Brian M.
-
p. 4059 - 4069
(2007/10/03)
-
- Mechanistic aspects of the C-H alkynylation reaction of acetylenic triflones. Determination of phenyl versus cyclohexyl migratory aptitude for a vinylidine carbene
-
13C-2 labeled phenyl ethynyl triflone undergoes regiospecific C-H alkynylation upon reaction with cyclohexane. The 13C label is found to be exclusively adjacent to the phenyl group in the product phenyl cyclohexyl acetylene, consistent with cyclohexyl radical addition at the α-position. Control studies show preferential phenyl migration from a vinylidine carbene, thus excluding the presence of such an intermediate.
- Xiang, Jason S.,Fuchs
-
p. 5269 - 5272
(2007/10/03)
-
- A Dynamic Equilibrium of Oxaphosphetanes
-
The course of the Wittig reaction was investigated by rapid injection NMR spectroscopy.Rate constants for the formation of oxaphosphetanes were determined.A new dynamic equilibrium of oxaphosphetanes was observed for the first time.The solvent and substituent dependence of the new effect was investigated.By labeling various oxaphosphetanes with 13C and 17O the lithium salt dependence of the new equilibrium was shown.A lithium adduct of oxaphosphetanes under these conditions is proposed. - Key Words: Wittig reaction / Rapid injection NMR / Dynamic NMR / Oxaphosphetanes
- Geletneky, Christian,Foersterling, Frank-Holger,Bock, Willi,Berger, Stefan
-
p. 2397 - 2402
(2007/10/02)
-
- The Photo-oxidation of meso-Tetraphenylporphyrins
-
The photo-oxidation of meso-tetraphenylporphyrin (TPP) dianion in methanol affords a purple benzoyl bilinone (5b) by addition of singlet oxygen, followed by ring-opening and addition of methanol; similar products (5a) and (5c) can be formed by addition of
- Cavaleiro, Jose A. S.,Neves, Maria G. P. S.,Hewlins, Michael J. E.,Jackson, Anthony H.
-
p. 1937 - 1943
(2007/10/02)
-
- DEOXYGENATION OF ALDEHYDES AND KETONES; A NEW GENERAL REACTION OF DIBROMOCARBENE AND DIBROMOCARBONYL YLIDES
-
The treatment of a variety of aldehydes and ketones with phenyl(tribromomethyl)mercury results in the production of carbon monoxide from the deoxygenation of the carbonyl group by dibromocarbene.
- Huan, Zhenwei,Landgrebe, John A.,Peterson, Kimberly
-
p. 2829 - 2832
(2007/10/02)
-
- Photochemistry of Some Deoxybenzoins in Micellar Solutions. Cage Effects, Isotope Effects, and Magnetic Field Effects
-
The photolyses of 1,2-diphenyl-2-methyl-1-propanone (1) and its D-, 13C-, and alkyl-substituted derivatives 2-5 in various micellar solutions have been investigated.It was found that the extent of cage disproportionation to yield benzaldehydes 6 and α-methylstyrenes 7 is enhanced by a factor of about 10 compared to the photolyses in homogeneous organic solvents.The advantage of using micelles rather than homogeneous solutions to enhance the magnitude of magnetic isotope and magnetic field effects on cage disproportionation is demonstrated.The results are interpreted in terms of a mechanism involving the competition between hyperfine-induced intersystem crossing of a triplet radical pair (3RP) to form a singlet radical pair (1RP) and escape of 3RP from the micelle.
- Turro, Nicholas J.,Mattay, Jochen
-
p. 4200 - 4204
(2007/10/02)
-
- Unambiguous Proof for Alcoxycarbonyl-group Migration in Wagner-Meerwein Rearrangements
-
In HSO3F/SO2ClF the β-hydroxy esters Ph-CHOH-CMe2-COOR (1, R=Me, Et) are doubly protonated, then transformed into the fluorosulfates 7 and (partly) into the fluorides 8.At -15 deg C, both 7 and 8 undergo a rearrangement, forming derivatives of Me2C=C(Ph)C
- Berner, Daniel,Dahn, Hans,Vogel, Pierre
-
p. 2538 - 2553
(2007/10/02)
-
- The Mechanism of Asymmetric Homogeneous Hydrogenation. Rhodium(I) Complexes of Dehydroamino Acids Containing Asymmetric Ligands Related to Bis(1,2-diphenylphosphino)ethane
-
The course of hydrogenation of dehydroamino acids by cationic rhodium complexes derived from bis(1,2-diphenylphosphino)ethane has been studied by phosphorus and carbon NMR.The parent complex reacts with hydrogen (1 atm) in methanol to form norbornane and
- Brown, John M.,Chaloner, Penny A.
-
p. 3040 - 3048
(2007/10/02)
-
- Geminal and Vicinal 13C-13C Coupling Constants in Carboxylic Acid Derivatives
-
Geminal 13C-13C coupling constants in αβ-unsaturated azlactones and the acids and esters derived from their hydrolysis are large and strongly dependent of configuration.Coupling constants in simple 13C1-labelled carboxylic acids are also reported; vicinal couplings show a strong geometric dependence but the geminal couplings depend mainly on hybridisation.
- Chaloner, Penny A.
-
p. 1028 - 1032
(2007/10/02)
-