Hypervalent Iodine Reagents Enable C-H Alkynylation with Iminophenylacetic Acids via Alkoxyl Radicals

Silver- and Base-Enabled SOMOphilic Alkynylation of Alkylboronic Acids with Bromoalkynes

Alkynyl-containing molecules hold significant importance in organic synthesis, drug discovery, and materials science. Herein, we report an efficient protocol for the C(sp)-C(sp3) cross-coupling of bromoalkynes with primary, secondary, and tertiary alkylboronic acids. Mechanistic experiments suggest that silver and base enable the generation of an alkyl radical intermediate from the alkylboronic acid and then undergo a cascade of α-addition and β-elimination with alkynyl bromides, leading to the construction of C(sp)-C(sp3) bonds. This strategy features readily available starting materials, diverse substrates, and mild and easily handled reaction conditions.

Remote radical alkynylation of unactivated C(sp3)-H bonds of ethynesulfonamides

We report an efficient protocol for the construction of δ-alkynyl amides via 1,5-hydrogen atom transfer and alkynyl group transfer of ethynesulfonamides. The readily installed ethynesulfonamides serve as both an amidyl radical precursor and an alkyne source. This reaction features excellent site selectivity for tertiary, secondary, primary, and benzylic C(sp3)-H bonds.

Free Alcohol-Mediated Radical Alkynylation and Allylation of Unactivated C(sp3)-H Bonds

The daunting challenges in converting alcoholic O-H bonds with high bond-dissociation energy (BDE) to alkoxy radicals and harnessing those unruly reaction species largely limit exploiting free alcohols in C(sp3)-H functionalization. Herein we describe a novel radical alkynylation and allylation of unactivated C(sp3)-H bonds with unmodified aliphatic alcohols. The use of phenyliodine bis(trifluoroacetate) (PIFA) enables the formation of alkoxy radicals under mild photochemical conditions. α-Methyl styrene serves as a sacrificial-reagent that significantly improves the reaction outcomes. This transition-metal free protocol further features broad substrate scope, exclusive site-selectivity, high product diversity, and simple operation, supplying a robust manifold for C(sp3)-H functionalization using easily available aliphatic alcohols as feedstock.

Scalable deoxygenative alkynylation of alcohols via flow photochemistry

Internal alkynes are often contained in bioactive pharmaceuticals and crucial intermediates in material sciences, yet their production methods are often limited and challenging, necessitating the development of more efficient and versatile synthetic routes. Here we report a method of deoxygenative alkynylation of alcohols via flow photochemistry. Formation of N-heterocyclic carbene-alcohol adducts undergoes oxidation by a photocatalyst, generating alkyl radicals. These radicals are subsequently trapped by an alkynylation agent, yielding the desired alkyne. Compared to batch reactions, the strategy using flow photochemistry is practical and efficient to complete the reaction in relatively short time with good yields. A wide range of functional groups were tolerated. The broad application of this method for alkyne synthesis in industry settings is anticipated, supported by the potential in late-stage functionalization of biomolecules and gram-scale synthesis.

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Preparation of a benziodazole-type iodine(III) compound and its application as a nitrating reagent for synthesis of furazans via a copper-catalyzed cascade process

The existing hypervalent I(III) reagents bearing ONO2 group are limited in types and their applications primarily focused on the nitrooxylation reactions featuring a fully-exo fashion. Herein, a benziodazole-type O2NO-I(III) compound was prepared and its reaction with β-monosubstituted enamines in the presence of CuI could trigger a radical nitration/cyclization/dehydration cascade to provide a series of less explored but biologically interesting furazan heterocycles. Mechanistically, the benziodazole-type O2NO-I(III) compound acts as a nitrating reagent and incorporates its NO moiety into the final furazan product in a fully-endo model, a process of which was proposed to involve nitration, cyclization and dehydration.

Synthesis of α-Trifluoromethyl Alkynes through Fluoroalkynylation of gem-Difluoroalkenes

A trifluoromethylalkynylation reaction of gem-difluoroalkenes with alkynyl sulfoxide by photoredox radical addition with good functional group tolerance in moderate to high yields, is developed for the synthesis of α-trifluoromethyl alkyne. This reaction features simple operation and inexpensive raw materials and provides an expeditious route to synthesize biologically relevant fluorine-containing alkynyl compounds with diverse structural skeletons.

Azido-alkynylation of alkenes through radical-polar crossover

We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

Recent progress in alkynylation with hypervalent iodine reagents

Although alkynes are one of the smallest functional groups, they are among the most versatile building blocks for organic chemistry, with applications ranging from biochemistry to material sciences. Alkynylation reactions have traditionally relied on the use of acetylenes as nucleophiles. The discovery and development of ethynyl hypervalent iodine reagents have allowed to greatly expand the transfer of alkynes as electrophilic synthons. In this feature article the progress in the field since 2018 will be presented. After a short introduction on alkynylation reactions and hypervalent iodine reagents, the developments in the synthesis of alkynyl hypervalent iodine reagents will be discussed. Their recent use in base-mediated and transition-metal catalyzed alkynylations will be described. Progress in radical-based alkynylations and atom-economical transformations will then be presented.

Hypervalent Iodine Reagents Enable C(sp2)-H Amidation of (Hetero)arenes with Iminophenylacetic Acids

Sulfonamide-containing (hetero)arenes are widely present in bioactive molecules. Here, we report the sulfonamidyl (hetero)arenes synthesis by the C(sp²)-H amidation from bench-stable amidyl-iminophenylacetic acids. The hypervalent iodine reagents covalently activated iminophenylacetic acids for the facile sulfonamidyl radical generation under mild photocatalytic oxidative conditions. Diversified indoles, pyrroles, imidazopyridines, and fused arenes underwent the C(sp²)-H amidation with excellent chemoselectivity and regioselectivity. This reaction performs well under neutral aqueous conditions with potential biological applications.