Contra-Thermodynamic Positional Isomerization of Olefins

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 144(1), P. 137 - 144

Published: Dec. 30, 2021

A light-driven method for the contra-thermodynamic positional isomerization of olefins is described. In this work, stepwise PCET activation a more substituted and thermodynamically stable olefin substrate mediated by an excited-state oxidant Brønsted base to afford allylic radical that captured Cr(II) cocatalyst furnish allylchromium(III) intermediate. situ protodemetalation allylchromium complex methanol highly regioselective affords isomerized less alkene product. The higher oxidation potential isomer renders it inert further oxidant, enabling accumulate in solution over course reaction. broad range isopropylidene substrates are accommodated, including enol ethers, enamides, styrenes, 1,3-dienes, tetrasubstituted alkyl olefins. Mechanistic investigations step also presented.

Language: Английский

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Stereodivergent, Kinetically Controlled Isomerization of Terminal Alkenes via Nickel Catalysis

Angewandte Chemie International Edition, Journal Year: 2024, Volume and Issue: 63(21)

Published: March 18, 2024

Abstract Because internal alkenes are more challenging synthetic targets than terminal alkenes, metal‐catalyzed olefin mono‐transposition (i.e., positional isomerization) approaches have emerged to afford valuable E ‐ or Z‐ from their complementary alkene feedstocks. However, the applicability of these methods has been hampered by lack generality, commercial availability precatalysts, and scalability. Here, we report a nickel‐catalyzed platform for stereodivergent / Z ‐selective synthesis at room temperature. Commercial reagents enable this one‐carbon transposition ‐internal via Ni−H‐mediated insertion/elimination mechanism. Though mechanistic regime is same in both systems, underlying pathways that lead each active catalysts distinct, with catalyst forming comproportionation an oxidative addition complex followed substrate protonation metal trialkylphosphonium salt additive. In case, ligand sterics denticity control stereochemistry prevent over‐isomerization.

Language: Английский

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Enantioselective Formal Vinylogous N–H Insertion of Secondary Aliphatic Amines Catalyzed by a High-Spin Cobalt(II) Complex

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(25), P. 9648 - 9656

Published: June 21, 2021

Vinylcarbene insertion into the nitrogen–hydrogen (N–H) bond of amines allows direct access to α,β-unsaturated γ-amino acid derivatives, meeting a marked challenge in control regio- and enantioselectivities. Here, we report highly γ-selective enantioselective N–H bonds aliphatic or aromatic secondary with vinyl substituted α-diazo pyrazoleamides using high-spin chiral N,N′-dioxide/cobalt(II) complex catalyst. The method affords wide variety valuable optically active Z- E-type amides. Calculation reveals spin state change from quartet cobalt(II) doublet Co(II)-carbene species for facile Z-selective nucleophilic addition.

Language: Английский

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Cobalt-Catalyzed Desymmetric Isomerization of Exocyclic Olefins

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(49), P. 20633 - 20639

Published: Dec. 6, 2021

Chiral cyclic olefins, 1-methylcyclohexenes, are versatile building blocks for the synthesis of pharmaceuticals and natural products. Despite prevalence these structural motifs, development efficient synthetic methods remains an unmet challenge. Herein we report a novel desymmetric isomerization exocyclic olefins using series newly designed chiral cobalt catalysts, which enables straightforward construction 1-methylcyclohexenes with diversified functionalities. The utility this methodology is highlighted by concise enantioselective product, β-bisabolene. versatility reaction products further demonstrated multifarious derivatizations.

Language: Английский

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Part per million levels of an anionic iron hydride complex catalyzes selective alkene isomerization via two-state reactivity

Chem Catalysis, Journal Year: 2021, Volume and Issue: 1(3), P. 631 - 647

Published: June 7, 2021

Language: Английский

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Spin effect on redox acceleration and regioselectivity in Fe-catalyzed alkyne hydrosilylation

National Science Review, Journal Year: 2023, Volume and Issue: 11(2)

Published: Dec. 19, 2023

ABSTRACT Iron catalysts are ideal transition metal because of the Earths abundant, cheap, biocompatible features iron salts. often have unique open-shell structures that easily undergo spin crossover in chemical transformations, a feature rarely found noble catalysts. Unfortunately, little is known currently about how structure and affect reactivity selectivity catalysts, which makes development low efficient trial-and-error program. In this paper, combination experiments theoretical calculations revealed iron-catalyzed hydrosilylation alkynes typical spin-crossover catalysis. Deep insight into electronic set well-defined active formal Fe(0) spin-delocalization between center 1,10-phenanthroline ligand effectively regulates center's oxidation state to meet opposite electrostatic requirements oxidative addition reductive elimination, respectively, essential for electron transfer process. The triplet was achieving high regioselectivity through tuning nonbonding interactions. These findings provide an important reference understanding effect catalyst on reaction. It inspiring other Earth-abundant especially from point view development.

Language: Английский

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(Z)-Selective Isomerization of 1,1-Disubstituted Alkenes by Scandium-Catalyzed Allylic C–H Activation

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(39), P. 26766 - 26776

Published: Sept. 20, 2024

The isomerization of 1,1-disubstituted alkenes through 1,3-hydrogen shift is an atom-efficient route for synthesizing trisubstituted alkenes, which are important moieties in many natural products, pharmaceuticals, and organic materials. However, this reaction often encounters regio- stereoselectivity challenges, typically yielding

Language: Английский

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Development and Mechanistic Studies of (E)-Selective Isomerization/Tandem Hydroarylation Reactions of Alkenes with a Nickel(0)/Phosphine Catalyst

ACS Catalysis, Journal Year: 2021, Volume and Issue: 11(11), P. 6741 - 6749

Published: May 26, 2021

A stereoselective alkene isomerization and sequential hydroarylation with arylboronic acid using a nickel(0) catalyst has been developed. The bulky monophosphine PAd2(n-Bu) is an effective ligand in these reactions to furnish both various stereo-defined internal alkenes products (isomerization: up 98%, E/Z = 98:2; tandem hydroarylation: 82%). Mechanistic studies based on experiments computational calculations suggested that the proceeds via intra- or intermolecular hydrogen shift. Furthermore, concerted multibond recombination boronic acid-assisted oxidative protometallation of was found be reasonable mechanism for formation alkylnickel(II) species from alkene, nickel(0), alcohol, hydroarylation.

Language: Английский

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Pincer Iron Hydride Complexes for Alkene Isomerization: Catalytic Approach to Trisubstituted (Z)-Alkenyl Boronates

ACS Catalysis, Journal Year: 2021, Volume and Issue: 11(16), P. 10138 - 10147

Published: July 30, 2021

An iron dichloride complex [Fe]Cl2 supported by a pincer phosphine–pyridine–imidazoline (PNNimid) ligand {[Fe]Cl2 = (PNNimid)FeCl2}, upon activation with NaHBEt3, catalyzes the isomerization of 1,1-disubstituted alkenyl boronates to synthetically valuable but previously difficult-to-access trisubstituted (Z)-alkenyl excellent regio- and stereoselectivity. The loading catalyst activator relative was found affect selectivity catalytic efficiency. In situ solvent-assisted electrospray ionization mass (SAESI-MS) studies revealed generation two catalytically competent species depending on Fe/NaHBEt3 ratios: reaction 1.5 equiv NaHBEt3 predominantly formed monohydride chloride [Fe]HCl, while treatment 3 furnished dihydride [Fe]H2. addition, alkyl intermediates resulting from insertion boronate into Fe–H bonds [Fe]HCl [Fe]H2 were successfully captured SAESI-MS. hydride catalysts are sensitive steric properties alkene substrates: is efficient for synthesis less hindered alkyl-bearing boronates, whereas favorable sterically more demanding aryl-substituted products. synthetic utility these products demonstrated stereoselective multisubstituted conjugated dienes cyercene A.

Language: Английский

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Catalytic 1,3-Proton Transfer in Alkenes Enabled by Fe═NR Bond Cooperativity: A Strategy for pK_a-Dictated Regioselective Transposition of C═C Double Bonds

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(22), P. 11978 - 11987

Published: May 25, 2023

Transition metal catalyzed alkene double bond transposition usually involves hydride intermediates. Despite significant advances in the design of catalysts that dictate product selectivity, control over substrate selectivity is less advanced and transition selectively transpose bonds substrates containing multiple 1-alkene functionalities are rare. Herein, we report three-coordinate high spin (S = 2) Fe(II) imido complex [Ph2B(tBuIm)2Fe═NDipp][K(18-C-6)THF2] (1-K(18-C-6)) catalyzes 1,3-proton transfer from to afford 2-alkene products. Mechanistic investigations involving kinetics, competition, isotope labeling studies, supported by experimentally calibrated DFT computations, strongly support an unusual nonhydridic mechanism for enabled cooperative action iron center basic ligand. As dictated pKa allylic protons, this catalyst enables regioselective C═C 1-alkenes. The state allows a wide scope functional groups be tolerated, including those typical poisons, such as amines, N-heterocycles, phosphines. These results demonstrate new strategy metal-catalyzed with predictable regioselectivity.

Language: Английский

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