1,721,113 research outputs found
Theoretical Study of Mechanism and Selectivity of Copper-Catalyzed C–H Bond Amidation of Indoles
No full textDensity functional theory calculations are used to study the reaction mechanism and origins of C2 selectivity in a copper(I)-catalyzed amidation of indoles. It is shown that concerted metalation−deprotonation is not able to reproduce the observed regioselectivity. Instead, an unprecedented mechanism based on a four-center reductive elimination is proposed to be responsible for the reaction outcome. This mechanism has a lower reaction barrier and is able to reproduce the experimentally observed selectivity. A possible alternative mechanism involving a Cu(II) species instead of Cu(III) is presented, but it is shown that higher energy barriers are associated with this mechanism. An important technical detail is that addition of dispersion effects to the B3LYP results is necessary to reproduce the observed selectivity, although not important for the overall mechanistic proposal.</p
Enantioselective Conjugate Silyl Additions to α,β-Unsaturated Aldehydes Catalyzed by Combination of Transition Metal and Chiral Amine Catalysts
No full textWe report that transition metal-catalyzed nucleophilic activation can be combined with chiral amine-catalyzed iminium activation as exemplified by the unprecedented enantioselective conjugate addition of a dimethylsilanyl group to alpha,beta-unsaturated aldehydes. These reactions proceed with excellent 1,4-selectivity to afford the corresponding beta-silyl aldehyde products 3 in high yields and up to 97:3 er using inexpensive bench stable copper salts and simple chiral amine catalysts. The reaction can also generate a quaternary stereocenter with good enantioselectivity. Density functional calculations are performed to elucidate the reaction mechanism and the origin of enantioselectivity.</p
Cationic Cyclization of 2-Alkenyl-1,3-dithiolanes: Diastereoselective Synthesis of <i>trans</i>-Decalins
No full textAn unprecedented and highly diastereoselective 6-endo-trig cyclization of 2-alkenyl-1,3-dithiolanes has been developed yielding trans-decalins, an important scaffold present in numerous di- and triterpenes. The novelty of this 6-endo-trig cyclization stands in the stepwise mechanism involving 2-alkenyl-1,3-dithiolane, acting as a novel latent initiator. It is suggested that the thioketal opens temporarily under the influence of TMSOTf, triggering the cationic 6-endo-trig cyclization, and closes after C−C bond formation and diastereoselective protonation to terminate the process. DFT calculations confirm this mechanistic proposal and provide a rationale for the observed diastereoselectivity. The reaction tolerates a wide range of functionalities and nucleophilic partners within the substrate. We have also shown that the one-pot 6-endo-trig cyclization followed by in situ 1,3-dithiolane deprotection afford directly the corresponding ketone. This improvement allowed the achievement of the shortest total synthesis of triptophenolide and the shortest formal synthesis of triptolide
UNRAVELLING THE MECHANISM OF THE GUERBET REACTION USING A RUTHENIUM CATALYST: A SYNERGISTIC COMPUTATIONAL AND EXPERIMENTAL STUDY
No full textUNRAVELLING THE MECHANISM OF THE GUERBET REACTION USING A RUTHENIUM CATALYST: A SYNERGISTIC COMPUTATIONAL AND EXPERIMENTAL STUDY
No full textSYNERGISTIC COMPUTATIONAL AND EXPERIMENTAL STUDY OF THE MECHANISM OF THE RU-CATALYSED GUERBET REACTION
No full textUnravelling the Mechanism of the Guerbet Reaction Catalyzed by a Ruthenium Catalyst: a Synergistic Computational and Experimental Study
No full textEnzyme-Like Catalysis via Ternary Complex Mechanism : Alkoxy-Bridged Dinuclear Cobalt Complex Mediates Chemoselective O-Esterification over N-Amidation
No full textHydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co-4(OCOR)(6)O](2) (2a: R = CF3, 2b: R = CH3, 2c: R = Bu-t) with nitrogen-containing ligands, such as 2,2'-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co-2((OCOBu)-Bu-t)(2)-(bpy)(2)(mu(2)-OCH2-C6H4-4-CH3)(2) (10), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis-Menten behavior of the complex 10 through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester.</p
Arylation with Unsymmetrical Diaryliodonium Salts : A Chemoselectivity Study
Full text linkPhenols, anilines, and malonates have been arylated under metal-free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti-ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents
Synthetic studies on the solanacol ABC ring system by cation-initiated cascade cyclization: implications for strigolactone biosynthesis
No full textWe report a new method for constructing the ABC ringsystem of strigolactones, in a single step from a simple linearprecursor by acid-catalyzed double cyclization. The reactionproceeds with a high degree of stereochemical control, whichcan be qualitatively rationalized usingDFT calculations. Ourconcise synthetic approach offers a new model for thinkingabout the (as yet) unknown chemistry that is employed in thebiosynthetic pathways leading to this class of plant hormones.</p
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