Practical and Regioselective Synthesis of C-4-Alkylated Pyridines

Journal of the American Chemical Society, Год журнала: 2021, Номер 143(31), С. 11927 - 11933

Опубликована: Июль 28, 2021

The direct position-selective C-4 alkylation of pyridines has been a long-standing challenge in heterocyclic chemistry, particularly from pyridine itself. Historically this addressed using prefunctionalized materials to avoid overalkylation and mixtures regioisomers. This study reports the invention simple maleate-derived blocking group for that enables exquisite control Minisci-type decarboxylative at allows inexpensive access these valuable building blocks. method is employed on variety different carboxylic acid alkyl donors, operationally scalable, applied known structures rapid fashion. Finally, work points an interesting strategic departure use Minisci chemistry earliest possible stage (native pyridine) rather than current dogma almost exclusively employs as late-stage functionalization technique.

Язык: Английский

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Photochemical aerobic oxidation of sulfides to sulfoxides: the crucial role of wavelength irradiation

Green Chemistry, Год журнала: 2022, Номер 24(10), С. 4108 - 4118

Опубликована: Янв. 1, 2022

Introducing green and sustainable photochemical aerobic protocols for the oxidation of sulfides to sulfoxides.

Язык: Английский

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Development of a Quinolinium/Cobaloxime Dual Photocatalytic System for Oxidative C–C Cross-Couplings via H₂ Release

ACS Catalysis, Год журнала: 2021, Номер 11(22), С. 14148 - 14158

Опубликована: Ноя. 8, 2021

Designing molecular photocatalysts for potent photochemical reactivities ranks among the most challenging but rewarding endeavors in synthetic photochemistry. Herein, we document a quinoline-based organophotoredox catalyst, 2,4-bis(4-methoxyphenyl)quinoline (DPQN2,4-di-OMe), that could be assembled via facile aldehyde–alkyne–amine (A3) couplings. Unlike reported photocatalysts, which impart their photoreactivities as covalently linked entities, our mechanistic studies suggested distinct proton activation mode of DPQN2,4-di-OMe. Simply upon protonation, DPQN2,4-di-OMe reach highly oxidizing excited state under visible-light irradiation (E*1/2 = +1.96 V vs standard calomel electrode, SCE). On this basis, synergistic merger and cobaloxime formulated an oxidative cross-coupling platform, enabling Minisci alkylation various C–C bond-forming reactions with diverse pool radical precursors absence chemical oxidants. The catalytic loading minimized to 0.025 mol % (TON 3360), polymer-supported photocatalyst, DPQN2,4-di-OR@PS, was prepared facilitate catalyst recycling (at 0.50 mmol up five times without significant loss photosynthetic efficiency).

Язык: Английский

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Brønsted acid-enhanced direct hydrogen atom transfer photocatalysis for selective functionalization of unactivated C(sp3)–H bonds

Nature Synthesis, Год журнала: 2022, Номер 1(10), С. 794 - 803

Опубликована: Авг. 4, 2022

Язык: Английский

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Enantioselective functionalization at the C4 position of pyridinium salts through NHC catalysis

Nature Communications, Год журнала: 2022, Номер 13(1)

Опубликована: Апрель 1, 2022

Abstract A catalytic method for the enantioselective and C4-selective functionalization of pyridine derivatives is yet to be developed. Herein, we report an efficient asymmetric β-pyridylations enals that involve N-heterocyclic carbene (NHC) catalysis with excellent control over enantioselectivity pyridyl C4-selectivity. The key strategy precise stereocontrol involves enhancing interactions between chiral NHC-bound homoenolate pyridinium salt in presence hexafluorobenzene, which effectively differentiates two faces radical. Room temperature sufficient this transformation, reaction efficiency further accelerated by photo-mediation. This methodology exhibits broad functional group tolerance enables facile access a diverse range enantioenriched β-pyridyl carbonyl compounds under mild metal-free conditions.

Язык: Английский

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Aliphatic C–H Functionalization Using Pyridine N-Oxides as H-Atom Abstraction Agents

ACS Catalysis, Год журнала: 2022, Номер 12(16), С. 10499 - 10505

Опубликована: Авг. 10, 2022

The alkylation and heteroarylation of unactivated tertiary, secondary, primary C(sp3)-H bonds was achieved by employing an acridinium photoredox catalyst along with readily available pyridine Noxides as hydrogen atom transfer (HAT) precursors under visible light. Oxygen-centered radicals, generated single-electron oxidation the Noxides, are proposed key intermediates whose reactivity can be easily modified structural adjustments. A broad range aliphatic C-H substrates electron-donating or -withdrawing groups well various olefinic radical acceptors heteroarenes were tolerated.

Язык: Английский

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Visible-light-induced metal-free coupling of C(sp³)–H sources with heteroarenes

Green Chemistry, Год журнала: 2022, Номер 24(8), С. 3056 - 3080

Опубликована: Янв. 1, 2022

This critical review chronologically summarizes the metal-free coupling methodologies of C(sp 3 )–H sources with heteroarenes induced by visible light. The articles which are published up to January 2022 on this topic enclosed here.

Язык: Английский

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Photochemical Organocatalytic Functionalization of Pyridines via Pyridinyl Radicals

Journal of the American Chemical Society, Год журнала: 2022, Номер 145(1), С. 47 - 52

Опубликована: Дек. 27, 2022

We report a photochemical method for the functionalization of pyridines with radicals derived from allylic C–H bonds. Overall, two substrates undergo to form new C(sp2)–C(sp3) bond. The chemistry harnesses unique reactivity pyridinyl radicals, generated upon single-electron reduction pyridinium ions, which effective coupling radicals. This novel mechanism enables distinct positional selectivity pyridine that diverges classical Minisci chemistry. Crucial was identification dithiophosphoric acid masters three catalytic tasks, sequentially acting as Brønsted protonation, single electron transfer (SET) reductant ion reduction, and hydrogen atom abstractor activation C(sp3)–H resulting then couple high regioselectivity.

Язык: Английский

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N-Amino pyridinium salts in organic synthesis

Organic Chemistry Frontiers, Год журнала: 2023, Номер 10(10), С. 2563 - 2580

Опубликована: Янв. 1, 2023

This review summarizes the synthesis and reactivity of N -aminopyridinium salts, discusses applications in organic synthesis, highlights potential for these reagents to enable novel synthetic disconnections innovations.

Язык: Английский

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C–H Functionalization of Pyridines via Oxazino Pyridine Intermediates: Switching to para-Selectivity under Acidic Conditions

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(28), С. 15581 - 15588

Опубликована: Июль 10, 2023

para-Selective C-H functionalization of pyridines holds a significant value but remains underdeveloped. Site-switchable under easily tunable conditions expedites drug development. We recently reported redox-neutral dearomatization-rearomatization strategy for meta-C-H via oxazino pyridine intermediates. Here, we demonstrate that these intermediates undergo highly para-selective simply by switching to acidic conditions. A broad scope para-alkylated and arylated is prepared through radical as well ionic pathways. These mild catalyst-free methods are applied the late-stage para-functionalization drugs using limiting reagents. Consecutive meta,para-difunctionalization also achieved with complete regiocontrol relying on pH-dependent reactivity pyridines.

Язык: Английский

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