Iron Catalyzed Dual-Oxidative Dehydrogenative (DOD) Tandem Annulation of Glycine Derivatives with Tetrahydrofurans

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp3)-H to construct C-C bonds

Ether derivatives are widespread as essential building blocks in various drugs, natural products, agrochemicals, and materials. Modern economy requires developing green strategies with improved efficiency and reduction of waste. Due to its atom and step-economy, the cross-dehydrogenative coupling (CDC) reaction has become a major strategy for ether functionalization. This review covers C-H/C-H cross-coupling reactions of ether derivatives with various C-H bond substrates via non-noble metal catalysts (Fe, Cu, Co, Mn, Ni, Zn, Y, Sc, In, Ag). We discuss advances achieved in these CDC reactions and hope to attract interest in developing novel methodologies in this field of organic chemistry.

Asymmetric Double Oxidative [3 + 2] Cycloaddition for the Synthesis of CF3-Containing Spiro[pyrrolidin-3,2'-oxindole]

An asymmetric double oxidative [3 + 2] cycloaddition is reported. Oxidation of 3-((2,2,2-trifluoroethyl)amino)indolin-2-ones and β-aryl-substituted aldehydes simultaneously and subsequent asymmetric cycloaddition in the presence of the chiral amino catalyst generated highly functionalized chiral CF₃-containing spiro[pyrrolidin-3,2'-oxindole] with four contiguous stereocenters stereoselectively, which is characterized by directly constructing two C-C bonds from four C(sp³)-H bonds. This new method features mild conditions, broad substrate scope, and excellent functional group compatibility.

Eosin-Y/Cu(OAc)2-catalyzed aerobic oxidative coupling reactions of glycine esters in the dark

Catalytic aerobic oxidative coupling reactions of glycine esters with β-keto acids, indoles, naphthols, and pyrrole have been realized at ambient temperature via the manipulation of the ground state reactivity of eosin-Y in the presence of Cu(OAc)₂ in the dark. This method delivers structurally diverse unnatural amino acid derivatives under mild reaction conditions. UV-vis absorption spectroscopy, cyclic voltammetry, X-ray photoelectron spectroscopy, high-resolution mass spectrometry, and control experiments were performed to formulate a plausible mechanistic pathway. The step economy, broad substrate scope, use of air as a green oxidant, and operationally simple set-up make this protocol highly appealing for both academic and industrial applications.

Dual C(sp3)-H Functionalization of Cyclic Ethers via Singlet Oxygen-Mediated Ring Opening and Ring Closing

A metal-free dual C(sp³)-H bond functionalization of saturated cyclic ethers via photooxidative singlet oxygen-mediated ring opening and ring closing has been developed, providing a method for generating hydrobenzofurans/pyrans/dioxins. Mechanistic studies have confirmed that ring-opening intermediates were effectively generated by singlet oxygen-mediated C(sp³)-H activation and efficiently reacted with aldehydes and activated methylene compounds to form a wide array of products with high diastereoselectivities (up to >95:5 dr). This study is a rare example of α,β-dual C(sp³)-H bond functionalization of ethers.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Iron-Catalyzed Oxidative Coupling of Indoline-2-ones with Aminobenzamides via Dual C-H Functionalization

We describe an unprecedented dual C-H functionalization of indolin-2-one via an oxidative C(sp³)-H/N-H/X-H (X = N, C, S) cross-coupling protocol, which is catalyzed by a simple iron salt under mild and ligand-free conditions and employs air (molecular oxygen) as the terminal oxidant. This method is readily applicable for the construction of tetrasubstituted carbon centers from methylenes and provides a wide variety of spiro N-heterocyclic oxindoles.

K2S2O8-HFIP synergistically promoted para-selective sp3 C-H bond diarylation of glycine esters

A metal-free K₂S₂O₈-HFIP synergistically promoted double Friedel-Crafts alkylation between a glycine derivative and N-substituted aniline was developed to efficiently synthesize diarylmethane derivatives with high para-selectivity. The reaction proceeded smoothly in the absence of any metal and ligand, and exhibited a good tolerance of functional groups.

Visible-Light-Mediated Aerobic Tandem Dehydrogenative Povarov/Aromatization Reaction: Synthesis of Isocryptolepines

A metal‐free, photoinduced aerobic tandem amine dehydrogenation/Povarov cyclization/aromatization reaction between N‐aryl glycine esters and indoles leads to tetracyclic 11H‐indolo[3,2‐c]quinolines under mild conditions and with high yields. The reaction can be performed by using molecular iodine along with visible light, or by combining an organic photoredox catalyst with a halide anion. Mechanistic studies reveal that product formation occurs through a combination of radical‐mediated oxidation steps with an iminium ion or N‐haloiminium ion [4+2]‐cycloaddition, and the N‐heterocyclic products constitute new analogues of the antiplasmodial natural alkaloid isocryptolepine.

One-electron oxidative dehydrogenative annulation and cyclization reactions

This review focuses on the recent advances in one-electron oxidation involved oxidative dehydrogenative annulations and cyclizations for the intermolecular and intramolecular construction of valuable ring structures.

Photoinduced iodine-mediated tandem dehydrogenative Povarov cyclisation/C–H oxygenation reactions

Visible light and iodine mediate dehydrogenative imine [4+2]-cycloaddition/C–H oxygenation reactions to furnish highly functionalised 3-quinolones under metal-free conditions.

Double-Oxidative Dehydrogenative [4+2]-Cyclization/Dehydrogenation/Oxygenation Tandem Reaction of N-Arylglycine Derivatives with Cumenes

Double-oxidative dehydrogenative (DOD) cyclization is one of the most straightforward strategies for the synthesis of cyclic compounds. A novel approach to substituted 3,4-dihydroquinoline-3-one derivatives via a Cu(II)/DDQ/O₂ system-catalyzed DOD [4+2]-cyclization/dehydrogenation/oxygenation cascade reaction of N-arylglycine derivatives, cumenes, and O₂ has been developed.

FeCl3-Catalyzed synthesis of pyrrolo[1,2-a]quinoxaline derivatives from 1-(2-aminophenyl)pyrroles through annulation and cleavage of cyclic ethers

A straightforward Fe-catalyzed method for the synthesis of pyrrolo[1,2-a]quinoxalines from 1-(2-aminophenyl)pyrroles and cyclic ethers, which includes functionalization of C(sp³)-H bonds and the construction of C-C and C-N bonds, has been developed. The features of this reaction are Fe catalysis, low-cost and readily accessible starting materials. Moreover, this procedure exhibits good functional group tolerance and a series of pyrrolo[1,2-a]quinoxaline derivatives are obtained in moderate to good yields.

Visible light-induced aerobic oxidative cross-coupling of glycine derivatives with indoles: a facile access to 3,3′ bisindolylmethanes

A rapid synthesis of 3,3′-bisindolylmethanes is achieved via a photocatalyzed double Friedel–Crafts alkylation reaction between glycine derivatives and indoles.

Metal-free photocatalyzed aerobic oxidative Csp3–H functionalization of glycine derivatives: one-step generation of quinoline-fused lactones

This reaction provides facile access to a series of valuable quinoline-fused lactones at room temperature under an air atmosphere.

Visible light-induced aerobic oxidative cross-coupling of glycine esters with α-angelicalactone: a facile pathway to γ-lactams

A rapid synthesis of substituted γ-lactams is achieved via metal-free photocatalyzed aerobic oxidative dehydrogenative formal [2 + 3] cyclization of glycine esters with α-angelicalactone.

Auto-oxidation promoted sp3 C–H arylation of glycine derivatives

An auto-oxidation promoted sp³ C–H arylation reaction between N-aryl glycine derivatives and electron-rich arenes, leading to the formation of N-aryl α-aryl α-amino acid derivatives, is described. This atom-economical and environmentally benign reaction proceeds smoothly under mild reaction conditions and requires only Brønsted acid and oxygen (balloon). A plausible radical involved mechanism is proposed.

Regiodivergent radical oxidative coupling of vinyl ethers with dithiane by copper or iron catalysis

Direct regioselective C–H dithioacetalization of readily available vinyl ethers to yield a variety of substituted dithianes under a copper or iron catalysis has been developed.

Oxidative couplings on tryptophan-based diketopiperazines leading to fused and bridged chemotypes

Selective C–C and C–N oxidative couplings on tryptophan-based diketopiperazines allow the direct access to two novel scaffolds.

Cross-dehydrogenative regioselective Csp3–Csp2coupling of enamino-ketones followed by rearrangement: an amazing formation route to acridine-1,8-dione derivatives

A novel route for the construction of acridine-1,8-dione derivatives through CDC coupling of enamino-ketones followed by rearrangement.