Decennary Update on Oxidative-Rearrangement Involving 1,2-Aryl C-C Migration Around Alkenes: Synthetic and Mechanistic Insights

In recent years, numerous methodologies on oxidative rearrangements of alkenes have been investigated, that produce multipurpose synthons and heterocyclic scaffolds of potential applications. The present review focused on recently established methodologies for oxidative transformation via 1,2-aryl migration in alkenes (2013-2023). Special emphasis has been placed on mechanistic pathways to understand the reactivity pattern of different substrates, challenges to enhance selectivity, the key role of different reagents, and effect of different substituents, and how they affect the rearrangement process. Moreover, synthetic limitations and future direction also have been discussed. We believe, this review offers new synthetic and mechanistic insight to develop elegant precursors and approaches to explore the utilization of alkene-based compounds for natural product synthesis and functional materials.

gem-Bromonitroalkane Involved Radical 1,2-Aryl Migration of α,α-Diaryl Allyl Alcohol TMS Ether via Visible-Light Photoredox Catalysis

A mild and efficient coupling method concerning the reactions of gem-bromonitroalkanes with α,α-diaryl allyl alcohol trimethylsilyl ethers was reported. A cascade consisting of visible-light-induced generation of an α-nitroalkyl radical and a subsequent neophyl-type rearrangement was key to realize the coupling reactions. Structurally diverse α-aryl-γ-nitro ketones, especially those bearing a nitrocyclobutyl structure, were prepared in moderate to high yields, which could be converted into spirocyclic nitrones and imines.

An Ionic-Radical Approach to Vicinally Functionalized Cyclopentanones and Cyclohexanones

A versatile strategy to access vicinally functionalized cyclopentanones and cyclohexanones is described. It takes advantage of new reagents, α-xanthyl enones, which can be prepared from the reaction of xanthate salts with the corresponding epoxyketones under mild conditions. β-Functionalization of these compounds can be performed by conjugate additions without affecting the xanthate moiety. This significantly expands the pool of xanthate substrates, allowing the synthesis of open chain and fused bicyclic building blocks useful in the synthesis of natural products.

Photocatalytic difluoromethylarylation of unactivated alkenes via a (hetero)aryl neophyl-like radical migration

Photoredox-catalyzed addition of the difluoromethylradical to unactivated alkenes has been found to trigger neophyl-like aryl and heteroaryl migrations which allowed the construction of a diverse series of difluoromethyl ketones. The reaction featured mild reaction conditions and broad substrate scope.

Halogen bond promoted aryl migration of allylic alcohols under visible light irradiation

A simple and catalyst-free radical addition/1,2-aryl migration cascade process of ally alcohol driven by halogen bond was developed under visible light irradiation, featuring mild conditions, practical procedures, and broad substrate scope.

Radical-mediated rearrangements: past, present, and future

Rearrangement reactions, one of the most significant transformations in organic chemistry, play an irreplaceable role in improving synthetic efficiency and molecular complexity. Concomitant cleavage and reconstruction of chemical bonds can display the great artistry and the glamour of synthetic chemistry. Over the past century, ionic rearrangement reactions, in particular those involving cationic pathways, have represented most of the research. Alongside the renaissance of radical chemistry, radical-mediated rearrangements have recently seen a rapid increase of attention from the chemical community. Many new radical rearrangements that extensively reveal the migratory behaviour of functional groups have been unveiled in the last decade. This Review provides a comprehensive perspective on the area from the past to present achievements, and brings up the prospects that may inspire colleagues to develop more useful synthetic tools based on radical rearrangements.

DTBP-promoted site-selective α-alkoxyl C-H functionalization of alkyl esters: synthesis of 2-alkyl ester substituted chromanones

The direct C-H functionalization of ethyl acetates was developed, delivering a variety of 1-(4-oxochroman-2-yl)ethyl acetate derivatives by reacting with chromones. This reaction has a wide substrate scope with excellent site-selective C-H activation at the inactive α-hydrogen of the alkoxyl group instead of the α-hydrogen of the carbonyl group under radical conditions. Compared with other protocols for the α-alkoxyl C-H functionalization of alkyl esters, a distinguishing feature of this reaction is that no metal catalyst was required, with DTBP as the sole oxidant.

Metal-free [3 + 2 + 1] annulation of allylic alcohols, ketones, and ammonium acetate: radical-involving synthesis of 2,3-diarylpyridine derivatives

A three-component [3 + 2 + 1] annulation strategy for the synthesis of biologically and pharmaceutically active 2,3-diarylpyridine derivatives by using a series of allylic alcohols, ketones, and ammonium acetate as substrates has been developed. The method proceeds efficiently under metal-free conditions, and the desired heterocycles could be obtained in a site-specific selectivity manner with good functional group tolerance.

Oxidative alkylation of alkenes with carbonyl compounds through concomitant 1,2-aryl migration by photoredox catalysis

An efficient protocol for the construction of 1,5-diketones was realized in the presence of organic fluorophore 4CzIPN, diaryliodonium salt, and visible light irradiation.

Free Radical Addition of Nitrile, Ketone, and Ester to Alkyne and the Selectivity Discussion

A general and practical atom transfer radical addition (ATRA) of simple nitriles, ketones, and esters to alkynes was developed. It can allow an efficient access to a wide range of β,γ-unsaturated nitriles, ketones, and esters. The unique chemoselectivity in this system is also discussed.

A copper-catalyzed radical coupling/fragmentation reaction: efficient access to β-oxophosphine oxides

The development of a novel copper-catalyzed three-component radical coupling/fragmentation cascade reaction to generate diverse β-oxophosphine oxides is reported.

Radical addition of ketones and cyanide to olefinsviaacid catalyzed formation of intermediate alkenyl peroxides

γ-Cyanoketones are formed by double radical addition from olefins, ketones and sulfonyl cyanidesviareactive alkenyl peroxide intermediates.

Regioselective Copper-Catalyzed Oxidative Coupling of α-Alkylated Styrenes with Tertiary Alkyl Radicals

A radical-mediated oxidative cross-coupling of readily accessible α-alkylated styrenes with 1,3-dicarbonyl compounds utilizing a combination of Cu(OAc)₂ and air as a catalytic system is described. Rather than requiring α-halocarbonyl compounds, this efficient approach enables direct installation of tertiary functionalized alkyl motifs to olefins with simple carbonyl derivatives. The novel protocol is characterized with high allylic selectivities via a competing β-H elimination. Both radical-clock and -trapping experiments provided clear-cut evidence for the intermediacy of an α-keto carbon-centered radical.

Metal-free oxidative radical cascade addition/oxobutylation of unactivated alkenes with acetone towards 3-(3-oxobutyl)indolines

A direct oxobutylation of N-allyl anilines with acetone was developed under metal-free and acid-free conditions.

Eosin Y-catalyzed, visible-light-promoted carbophosphinylation of allylic alcohols via a radical neophyl rearrangement

An eosin Y-catalyzed, visible-light-promoted phosphinylation-induced 1,2-rearrangement reaction of allylic alcohols to prepare various β-aryl-γ-ketophosphine oxides is presented.

Iron-Promoted Difunctionalization of Alkenes by Phenylselenylation/1,2-Aryl Migration

Iron-promoted difunctionalization of α,α-diaryl and α-aryl-α-alkyl allylic alcohols has been efficiently achieved by means of N-(phenylseleno)phthalimide (N-PSP) under mild conditions. An in situ generated phenylselenium cation (PhSe⁺) was added to the olefinic C═C bond to initiate the regioselective phenylselenylation with concomitant 1,2-aryl migration, following a migration preference contrary to the well-known radical pathway. Hydrazonation of the resultant alkene difunctionalization products, that is, α-aryl-β-phenylselenyl ketones, and subsequent copper-catalyzed dehydroselenylation efficiently afforded functionalized 2-pyrazoline derivatives.

Recent Advances in Radical C-H Activation/Radical Cross-Coupling

Research and industrial interest in radical C-H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C-H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M-R groups, and coupling of radical cations with nucleophiles (Nu).

Direct Assembly of Prenylated Heteroarenes through a Cascade Minisci Reaction/Dehydration Sequence

The prenyl group is an important component in bioactive compounds. Herein, we report the assembly of prenylated heteroarenes through a cascade Minisci reaction and acid-promoted dehydration sequence. The use of potassium (3-hydroxy-3-methylbut-1-yl)trifluoroborate as a new coupling reagent allows the direct introduction of prenyl and 3-hydroxy-3-methylbutyl groups to a wide variety of electron-deficient heteroarenes. Synthetic application is also demonstrated.

Metal-free oxidative functionalization of C(sp3)–H of ketones and alcohols for the synthesis of isoquinolinonediones

A metal-free alkyl radical induced addition/cyclization reaction of acrylamide has been developed.

Fe(iii)-mediated isomerization of α,α-diarylallylic alcohols to ketones via radical 1,2-aryl migration

An Fe(iii)-mediated radical 1,2-aryl migration of α,α-diarylallylic alcohols for the isomerization to ketones is described.