Copper-Promoted Oxidative Coupling of Enamides and Alkynes for the Synthesis of Substituted Pyrroles

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Mild and Efficient Copper-Catalyzed Synthesis of Trisubstituted Pyrroles

A sustainable and time economic approach has been developed for the synthesis of polysubstituted pyrroles using copper iodide as a catalyst. The reaction proceeded through imine formation followed by cyclization with alkyne-Cu intermediate, which was supported by control experiments studies. The newly formed substituted pyrroles were obtained in excellent yields with high regioselectivity under mild conditions.

Alkynoates as Versatile and Powerful Chemical Tools for the Rapid Assembly of Diverse Heterocycles under Transition-Metal Catalysis: Recent Developments and Challenges

Heterocycles, heteroaromatics and spirocyclic entities are ubiquitous components of a wide plethora of synthetic drugs, biologically active natural products, marketed pharmaceuticals and agrochemical targets. Recognizing their high proportion in drugs and rich pharmacological potential, these invaluable structural motifs have garnered significant interest, thus enabling the development of efficient catalytic methodologies providing access to architecturally complex and diverse molecules with high atom-economy and low cost. These chemical processes not only allow the formation of diverse heterocycles but also utilize a range of flexible and easily accessible building units in a single operation to discover diversity-oriented synthetic approaches. Alkynoates are significantly important, diverse and powerful building blocks in organic chemistry due to their unique and inherent properties such as the electronic bias on carbon-carbon triple bonds posed by electron-withdrawing groups or the metallic coordination site provided by carbonyl groups. The present review highlights the comprehensive picture of the utility of alkynoates (2007-2019) for the synthesis of various heterocycles (> 50 types) using transition-metal catalysts (Ru, Rh, Pd, Ir, Ag, Au, Pt, Cu, Mn, Fe) in various forms. The valuable function of versatile alkynoates (bearing multifunctional groups) as simple and useful starting materials is explored, thus cyclizing with an array of coupling partners to deliver a broad range of oxygen-, nitrogen-, sulfur-containing heterocycles alongside fused-, and spiro-heterocyclic compounds. In addition, these examples will also focus the scope and reaction limitations, as well as mechanistic investigations into the synthesis of these heterocycles. The biological significance will also be discussed, citing relevant examples of drug molecules highlighting each class of heterocycles. This review summarizes the recent developments in the synthetic methods for the synthesis of various heterocycles using alkynoates as readily available starting materials under transition-metal catalysis.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Iodine-catalyzed diazo activation to access radical reactivity

Transition-metal-catalyzed diazo activation is a classical way to generate metal carbene, which are valuable intermediates in synthetic organic chemistry. An alternative iodine-catalyzed diazo activation is disclosed herein under either photo-initiated or thermal-initiated conditions, which represents an approach to enable carbene radical reactivity. This metal-free diazo activation strategy were successfully applied into olefin cyclopropanation and epoxidation, and applying this method to pyrrole synthesis under thermal-initiated conditions further demonstrates the unique reactivity using this method over typical metal-catalyzed conditions.

Synthesis of multisubstituted pyrroles by nickel-catalyzed arylative cyclizations of N-tosyl alkynamides

The synthesis of multisubstituted pyrroles by the nickel-catalyzed reaction of N-tosyl alkynamides with arylboronic acids is reported.

Pd-Catalyzed oxidative annulation of enamides with diazabicyclic olefins: rapid access to cyclopentene fused 2-pyrrolines

A catalytic tandem transformation via C–H activation of enamides for the stereoselective synthesis of cyclopentene fused 2-pyrrolines has been realized.

Novel and efficient transformation of enamides into α-acyloxy ketones via an acyl intramolecular migration process

Hydrogen peroxide and anhydride mediated transformation of enamides to afford substituted α-acyloxy ketones is described.

A new avenue to the synthesis of highly substituted pyrroles: synthesis from N-propargylamines

Pyrroles have attracted much attention due to their potential biological activities.

Recent developments in the group-1B-metal-catalyzed synthesis of pyrroles

Pyrroles are important synthetic targets as a result of their occurrence in numerous biologically active molecules, their important roles in diverse living processes, and their utility as versatile intermediates.

A facile and efficient method for the synthesis of 1,2,4-trisubstituted imidazoles with enamides and benzylamines

A novel and practical method for the construction of 1,2,4-trisubstituted imidazoles with enamides and benzylamines catalysed by CuBr and I₂ has been developed.

Cobalt(iii)-catalyzed synthesis of pyrroles from enamides and alkynes

An efficient and regioselective cobalt-catalyzed synthesis of multi-substituted pyrroles is reported by the use of readily available enamides and alkynes.

Synthesis of 2,5-disubstituted pyrroles via dehydrogenative condensation of secondary alcohols and 1,2-amino alcohols by supported platinum catalysts

2,5-Disubstituted pyrroles are synthesized by acceptorless dehydrogenative reaction of 1,2-aminoalcohols and secondary alcohols by Pt/carbon catalyst.

Synthesis of oxazoles by silver catalysed oxidative decarboxylation–cyclization of α-oxocarboxylates and isocyanides

This work developed a silver catalysed synthesis of oxazoles by the oxidative decarboxylation–cyclization of α-oxocarboxylates and isocyanides.

Direct metal-catalyzed regioselective functionalization of enamides

Enamides are stable enamine surrogates and provide key intermediates for the synthesis of small but complex nitrogen-containing compounds. Metal-catalyzed regioselective functionalization of enamides provides a rapid method to synthesize useful nitrogen containing heterocycles. This review discloses the recent progress made in the development of the C-H functionalization of enamides involving efficient and atom-economical routes. Syntheses of different heterocycles are classified based on the site reactivity of enamides and key mechanistic insights are given for each transformation.

Reaction of α-amido sulfones with functionalized nitrocompounds: a new two-step synthesis of N-alkoxycarbonyl-2,5-disubstituted pyrroles

N-Alkoxycarbonyl-2,5-disubstituted pyrroles can be readily prepared by a new two-step procedure involving a preliminary addition of nitro ketals to α-amido sulfones followed by an acid promoted ring closure of the obtained intermediates through a cascade process.