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ABSTRACT: The origin of the high levels of reactivity and diastereoselectivity (>99:1 dr) observed in the oxazoline-directed, Pd(II)-catalyzed sp(3) C-H bond iodination and acetoxylation reactions as reported in previous publications has been studied and explained on the basis of experimental and computational investigations. The characterization of a trinuclear chiral C-H insertion intermediate by X-ray paved the way for further investigations into C-H insertion step through the lens of stereochemistry. Computational investigations on reactivities and diastereoselectivities of C-H activation of t-Bu- and i-Pr-substituted oxazolines provided good agreement with the experimental results. Theoretical predictions with DFT calculations revealed that C-H activation occurs at the monomeric Pd center and that the most preferred transition state for C-H activation contains two sterically bulky t-Bu substituents in anti-positions due to steric repulsion and that this transition state leads to the major diastereomer, which is consistent with the structure of the newly characterized C-H insertion intermediate. The structural information about the transition state also suggests that a minimum dihedral angle between C-H bonds and Pd-OAc bonds is crucial for C-H bond cleavage. We have also utilized density functional theory (DFT) to calculate the energies of various potential intermediates and transition states with t-Bu- and i-Pr-substituted oxazolines and suggested a possible explanation for the substantial difference in reactivity between the t-Bu- and i-Pr-substituted oxazolines.
Journal of the American Chemical Society 07/2012; 134(34):14118-26. · 9.91 Impact Factor
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ABSTRACT: A series of Cu(I)-amido complexes both lacking ancillary ligands and containing 1,10-phenanthroline (phen) as ancillary ligand have been prepared. These complexes react with iodoarenes to form arylamine products, and this reactivity is consistent with the intermediacy of such complexes in catalytic Ullmann amination reactions. The stoichiometric reactions of the Cu(I)-amido complexes with iodoarenes are autocatalytic, with the free CuI generated during the reaction serving as the catalyst. Such autocatalytic behavior was not observed for reactions of iodoarenes with copper(I) amidates, imidates, or phenoxides. The selectivity of these complexes for two sterically distinct aryl halides under various conditions imply that the autocatalytic reaction proceeds by forming highly reactive [CuNPh(2)](n) lacking phen. Reactions with radical probes imply that the reactions of phen-ligated Cu(I)-amido complexes with iodoarenes occur without the intermediacy of aryl radicals. Density functional theory calculations on the oxidative addition of iodoarenes to Cu(I) species are consistent with faster reactions of iodoarenes with CuNPh(2) species lacking phen in DMSO than reactions of iodoarenes with LCuNPh(2) in which L = phen. The free-energy barrier computed for the reaction of PhI with (DMSO)CuNPh(2) was 21.8 kcal/mol, while that for the reaction of PhI with (phen)CuNPh(2) was 33.4 kcal/mol.
Journal of the American Chemical Society 10/2010; 132(45):15860-3. · 9.91 Impact Factor
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Angewandte Chemie International Edition 03/2010; 49(12):2185-9. · 13.45 Impact Factor
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ABSTRACT: A Pd(II)-catalyzed reaction protocol for the carboxylation of ortho-C-H bonds in anilides to form N-acyl anthranilic acids has been developed. This reaction procedure provides a novel and efficient strategy for the rapid assembly of biologically and pharmaceutically significant molecules, such as benzoxazinones and quinazolinones, from simple anilides without installing and removing an external directing group. The reaction conditions are also amenable to the carboxylation of N-phenyl pyrrolidinones. A monomeric palladacycle containing p-toluenesulfonate as an anionic ligand has been characterized by X-ray crystallography, and the crucial role of p-toluenesulfonic acid in the activation of C-H bonds in the presence of carbon monoxide is discussed. Identification of two key intermediates, a mixed anhydride and benzoxazinone formed by reductive elimination from organometallic Ar(CO)Pd(II)-OTs species, provides mechanistic evidence for a dual-reaction pathway.
Journal of the American Chemical Society 12/2009; 132(2):686-93. · 9.91 Impact Factor
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ABSTRACT: This critical review discusses historical and contemporary research in the field of transition metal-catalyzed carbon-hydrogen (C-H) bond activation through the lens of stereoselectivity. Research concerning both diastereoselectivity and enantioselectivity in C-H activation processes is examined, and the application of concepts in this area for the development of novel carbon-carbon and carbon-heteroatom bond-forming reactions is described. Throughout this review, an emphasis is placed on reactions that are (or may soon become) relevant in the realm of organic synthesis (221 references).
Chemical Society Reviews 11/2009; 38(11):3242-72. · 28.76 Impact Factor
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ChemInform 01/2009; 40(10).
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ABSTRACT: A Pd(II)-catalyzed reaction protocol for the direct carboxylation of benzoic and phenylacetic acid derivatives to form dicarboxylic acids has been developed. The reaction conditions are also applicable for the carboxylation of vinyl C-H bonds. The first C-H insertion Pd-aryl complex from carboxylic acids has been characterized by X-ray crystallography.
Journal of the American Chemical Society 11/2008; 130(43):14082-3. · 9.91 Impact Factor
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ABSTRACT: O-Methyl hydroxamic acids, readily available from carboxylic acids, are found to be extremely reactive for beta-C-H activation by Pd(OAc)2. This reactivity is exploited to develop the first example of cross-coupling sp3 C-H bonds with sp3 boronic acids. Air was shown to be a suitable stoichiometric oxidant for the catalytic oxidative coupling reaction. A biologically active natural product is readily converted to its novel analogues through this coupling reaction.
Journal of the American Chemical Society 07/2008; 130(23):7190-1. · 9.91 Impact Factor
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ABSTRACT: Pd(OAc)2-mediated dehydrogenation of an alkyl group to a double bond or a η3-allylic complex via sp3 C−H bond activation and allylic oxidation is reported. A novel redox is proposed for this double oxidation under oxidant-free conditions. A catalytic protocol using benzoquinone as the stoichiometric oxidant has also been developed for the dehydrogenation of cyclopentylcarboxamides.
03/2008;
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Angewandte Chemie International Edition 01/2008; 47(28):5215-9. · 13.45 Impact Factor
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ABSTRACT: The use of preformed sodium carboxylates as substrates led to the first observation of facile Pd-insertions into sp3 β-C−H bonds in simple aliphatic acids. Consequently, Pd-catalyzed methylation and arylation of o-C−H bonds in benzoic acids and β-C−H bonds in aliphatic acids using either a phenylboronate, methylboronic acid, or ArI have been achieved via a C−H activation/C−C coupling sequence.
Journal of the American Chemical Society 04/2007; 129(12):3510-1. · 9.91 Impact Factor
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ABSTRACT: A novel route to the synthesis of cyclopropane derivatives is described. 1,1-Dimethyls in 2-(1,1-dimethylalkyl)dimethyloxazolines are first converted into 1,3-diiodide derivatives via Pd-catalyzed sequential C-H activation and then radically cyclized to provide 2-(1-alkylcylclopropyl)dimethyloxazolines. The use of EtOAc as a solvent is crucial for the diiodination of the functionalized substrates. [reaction: see text]
Organic Letters 01/2007; 8(25):5685-8. · 5.86 Impact Factor
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ABSTRACT: Recent progress in sigma-chelation directed C-H functionalization from the authors' group is described to illustrate the challenges and opportunities in the development of synthetically-useful catalytic reactions involving C-H activation as the key step. Emphasis is placed on strategies for developing catalysis under mild conditions and controlling regio- and stereoselectivity.
Organic & Biomolecular Chemistry 12/2006; 4(22):4041-7. · 3.70 Impact Factor
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Angewandte Chemie International Edition 01/2006; 44(45):7420-4. · 13.45 Impact Factor
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Angewandte Chemie International Edition 04/2005; 44(14):2112-5. · 13.45 Impact Factor
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ABSTRACT: A Cu(II)/I2-mediated C–H bond activation is described. A variety of 2-phenylpyridine derivatives are oxidatively dimerized at the ortho-position of the phenyl ring in which a net loss of two hydrogen atoms results in the formation of a biaryl compound via a double C–H activation/C–C bond-forming process. Moderate functional group tolerance was observed on both the aryl and the pyridyl rings. A single electron transfer (SET) or electrophilic metalation process for iodination followed by Ullmann coupling of the intermediate iodinated product is proposed as the operating mechanism for the dimerization process.Graphical abstract
Tetrahedron. 65(16):3085-3089.
