Phenyliodine bis(trifluoroacetate) as a sustainable reagent: exploring its significance in organic synthesis

Iodine-containing molecules, especially hypervalent iodine compounds, have gained significant attention in organic synthesis. They are valuable and sustainable reagents, leading to a remarkable surge in their use for chemical transformations. One such hypervalent iodine compound, phenyliodine bis(trifluoroacetate)/bis(trifluoroacetoxy)iodobenzene, commonly referred to as PIFA, has emerged as a prominent candidate due to its attributes of facile manipulation, moderate reactivity, low toxicity, and ready availability. PIFA presents an auspicious prospect as a substitute for costly organometallic catalysts and environmentally hazardous oxidants containing heavy metals. PIFA exhibits remarkable catalytic activity, facilitating an array of consequential organic reactions, including sulfenylation, alkylarylation, oxidative coupling, cascade reactions, amination, amidation, ring-rearrangement, carboxylation, and numerous others. Over the past decade, the application of PIFA in synthetic chemistry has witnessed substantial growth, necessitating an updated exploration of this field. In this discourse, we present a concise overview of PIFA's applications as a 'green' reagent in the domain of synthetic organic chemistry. A primary objective of this article is to bring to the forefront the scientific community's awareness of the merits associated with adopting PIFA as an environmentally conscientious alternative to heavy metals.

PIDA/I2-mediated photo-induced aerobic N-acylation of sulfoximines with methylarenes

A visible-light-promoted, PIDA/I2-mediated acylation of NH-sulfoximines with methylarenes as an acyl source has been achieved. This transition metal and photosensitizer-free approach provides easy access to N-acylsulfoximines via oxidative coupling of sulfoximines with easily available methylarenes without using any peroxide source. Mechanistic investigations suggest the intermediacy of radicals and the importance of molecular oxygen.

Synthetic Electrochemistry Enabled Esterification via Oxidative Mesolytic Cleavage of Alkoxyamines

Stable benzylic carbocations were generated via mesolytic cleavage of TEMPO-derived alkoxyamines, which was realized by electrochemical oxidation. This strategy provided an efficient and unique approach to access stabilized carbocations under mild conditions. Esterification of benzylic carbocations using carboxylic acid produced a variety of benzylic esters with a broad substrate scope and excellent functional group compatibility.

A novel quinoline-based NNN-pincer Cu(II) complex as a superior catalyst for oxidative esterification of allylic C(sp3)-H bonds

We report for the first time that the quinoline-based NNN-pincer Cu(II) complex acts as an air stable superior catalyst for the oxidative cross-coupling of the allyl sp³ C-H bond with an acid for the synthesis of allyl esters in a homogeneous system at ambient temperature. The synthesized catalyst, 1, has been well characterized by various analytical techniques (HRMS, single crystal X-ray diffraction, CV, EPR, UV-vis spectroscopy) and showed excellent catalytic activity for the oxidative esterification of allylic C(sp³)-H bonds at 40 °C within a very short period of time (1 h) using only 1 mol% of the catalyst. A wide variety of aromatic allylic esters were synthesized in moderate to good yields, which could be extended to aliphatic allyl esters as well.

From methylarenes to Esters: Efficient oxidative Csp3-H activation promoted by CuO decorated magnetic reduced graphene oxide

Magnetic reduced graphene oxide supported CuO (rGO/Fe3O4-CuO) as the heterogeneous catalyst in cross dehydrogenative coupling (CDC) reactions has been demonstrated for the synthesis of esters using methyl aromatics, aldehydes/benzyl alcohols...

FeIII/TBHP mediated remote C–O bond construction of 8-aminoquinolines: access to methoxylation and cyanomethoxylation

The C5 regioselective methoxylation and cyanomethoxylation of 8-aminoquinolines were achieved under FeIII/TBHP system by tuning the temperature and solvent. TBHP was investigated as an “oxygen” source in the ether bond formation for the first time.

The Rich Legacy and Bright Future of Transition-Metal Catalyzed Peroxide Based Radical Reactions

This personal account is mainly focused on the author's involvement in the field of transition metal-catalyzed peroxide based radical reactions. Over the past decades, radical chemistry has flourished and become crucial in contemporary synthetic organic chemistry. Owing to the presence of a single electron in one orbital, radicals are very unstable and react very fast. To carry out desired transformations and to control the side reactions the stabilizations of these radicals is essential. Fortunately, the implementation of a suitable transition metal and peroxide combination into the radical reactions have proved beneficial. Transition metals not only stabilizes the radicals but also protects them from being quenched by undesired homo-coupling or fragmentation. Transition metal-catalyzed radical-radical reactions provide an innovative way for the construction and derivatization of carbocycles and heterocycles. The objective of this review is to give an overview of the construction and derivatization of heterocycles through the lens of radical chemistry, mainly focusing on research work done by our group.

Regio- and Stereoselective (SN2) N-, O-, C- and S-Alkylation Using Trialkyl Phosphates

Bimolecular nucleophilic substitution (SN2) is one of the most well-known fundamental reactions in organic chemistry to generate new molecules from two molecules. In principle, a nucleophile attacks from the back side of an alkylating agent having a suitable leaving group, most commonly a halide. However, alkyl halides are expensive, very harmful, toxic and not so stable, which makes them problematic for laboratory use. In contrast, trialkyl phosphates are inexpensive, readily accessible and stable at room temperature, under air, and are easy to handle, but rarely used as alkylating agents in organic synthesis. Here, we describe a mild, straightforward and powerful method for nucleophilic alkylation of various N-, O-, C- and S-nucleophiles using readily available trialkyl phosphates. The reaction proceeds smoothly in excellent yield, and quantitative yield in many cases, and covers a wide range of substrates. Further, the rare stereoselective transfer of secondary alkyl groups has been achieved with inversion of configuration of chiral centers (up to 98% ee).

Ultrasound accelerated synthesis of O-alkylated hydroximides under solvent- and metal-free conditions

A novel, sustainable, environmentally friendly, high substrate scope, efficient, solvent-free and metal catalyst-free method for the cross-dehydrogenative coupling (CDC) reaction between N-hydroxyphthalimide (NHPI) and benzyl/ether compounds is described. This coupling reaction proceeds through ultrasound acceleration. Compared to conventional heating conditions, the use of ultrasound techniques not only improves the reaction efficiency and enhances the reaction rate but also minimizes the side reactions.

C-H functionalisation of cycloalkanes

Among organic compounds hydrocarbons are inexpensive and possibly the most abundant among natural resources. Developing strategies for selective functionalisation of inert hydrocarbon C-H bonds is one of the most ideal synthetic paths that a synthetic chemist could think of. This critical review focuses on the recent development of various directed and non-directed cycloalkylations leading to the formation of carbon-carbon (C-C) and carbon-heteroatom (C-X) bonds. Apart from various transition metal catalysed cycloalkylations, this review also covers various metal-free cycloalkylation processes.

Directing activator-assisted regio- and oxidation state-selective aerobic oxidation of secondary C(sp(3))-H bonds in aliphatic alcohols

The regioselective conversion of an unactivated C(sp(3))-H bond of a methylene carbon (CH2) into a C-O single bond is an attractive reaction in organic synthesis. Herein, we present a strategy for a regio- and oxidation state-selective aerobic C-H oxidation based on an N-hydroxyamide-derived directing activator (DA), which is attached to a hydroxy group in alcohol substrates. The DA reacts with NOx species generated in situ from NaNO2, a Brønsted acid, and aerobic oxygen, and effectively generates an amidoxyl radical from the N-hydroxy moiety of the DA. Then, the amidoxyl radical promotes site-selective intramolecular C-H abstraction from methylenes with γ- (or δ-) selectivity. The thus-generated methylene radicals are trapped by molecular oxygen and NO. This process results in the predominant formation of nitrate esters as products, which suppresses undesired overoxidation. The products can be easily converted into alcohols after hydrogenolysis.

KI-catalyzed oxidative cyclization of α-keto acids and 2-hydrazinopyridines: efficient one-pot synthesis of 1,2,4-triazolo[4,3-a]pyridines

A one-pot approach to 1,2,4-triazolo[4,3-a]pyridines via KI-catalyzed oxidative cyclization was developed with good economical and environmental advantages.

Copper-catalyzed α-C–H acyloxylation of carbonyl compounds with terminal alkynes

Herein, a copper/TBHP catalyst system for the α-C–H acyloxylation of carbonyl compounds is developed using terminal alkynes as the acyloxy source.

Visible-Light Mediated Oxidative C-H/N-H Cross-Coupling between Tetrahydrofuran and Azoles Using Air

Tetrahydrofuran is a privileged structural moiety in many important organic compounds. In this work, we have developed a simple and mild catalytic oxidative amination of tetrahydrofuran mediated by visible-light catalysis. The C(sp3)-H bond of tetrahydrofuran was activated using molecular oxygen as a benign oxidant. Besides, a variety of azoles could be tolerated, providing a green route for N-substituted azoles.

TBHP-mediated highly efficient dehydrogenative cross-oxidative coupling of methylarenes with acetanilides

A TBHP-mediated dehydrogenative cross-oxidative-coupling approach has been developed for the synthesis of N-arylbenzamides from methylarenes and acetanilides. This cross-coupling method is free of transition metal catalysts and ligands, and no extra organic solvents are required, which make it an useful and attractive strategy for the straightforward construction of C–N bonds. Besides, this conversion is an important complement to the conventional C–N forming strategies.

Copper porphyrin catalyzed esterification of C(sp3)–H via a cross-dehydrogenative coupling reaction

Copper porphyrin was an efficient catalyst for the direct esterification of C(sp³)–H bonds using DTBP as an oxidant.

Reusable ionic liquid-catalyzed oxidative esterification of carboxylic acids with benzylic hydrocarbons via benzylic Csp3–H bond activation under metal-free conditions

A protocol for oxidation of the Csp³–H bond in benzylic hydrocarbons with carboxylic acids using ionic liquid as reusable catalyst has been reported.

I2/TBHP-mediated oxidative coupling of ketones and toluene derivatives: a facile method for the preparation of α-benzoyloxy ketones

Synthesis of α-benzoyloxy ketones from ketones and toluenes using TBHP as the surrogate of toxic heavy-metal oxidants and the oxygen source of the incorporated oxygen.

Catalyst-Free sp3 C-H Acyloxylation: Regioselective Synthesis of 1-Acyloxy Derivatives of the Natural Product Tanshinone IIA

Tanshinone IIA is a valuable bioactive natural product isolated from the well-known Chinese herb Danshen. Structural manipulation of the A-ring of tanshinone IIA is rather limited. In this study, a substrate tautomerization-induced catalyst-free benzylic sp³ C-H acyloxylation approach is reported that allows the direct introduction of various acyloxy groups at the A-ring benzylic methylene of various tanshinone IIA substrates, thus avoiding the use of expensive transition metal catalysts and the production of harmful byproducts. This approach features a unique acid-induced reversible enolization/oxa-conjugate addition process followed by oxidation to exclusively give a series of diverse 1-acyloxylated derivatives under simple conditions in a regioselective manner. Compared with the literature procedures, this protocol demonstrates a higher efficiency, a more robust functional-group tolerance, atom economy, and lower cost.

Efficient photolytic C-H bond functionalization of alkylbenzene with hypervalent iodine(iii) reagent

A practical approach to radical C-H bond functionalization by the photolysis of a hypervalent iodine(iii) reagent is presented. The photolysis of [bis(trifluoroacetoxy)iodo]benzene (PIFA) leads to the generation of trifluoroacetoxy radicals, which allows the smooth transformation of various alkylbenzenes to the corresponding benzyl ester compounds under mild reaction conditions.