Selective C(sp3)-C(sp3) Cleavage/Alkynylation of Cycloalkylamides Enables Aminoalkyne Synthesis with Hypervalent Iodine Reagents

Cooperative Photoredox and Cobalt-Catalyzed Acceptorless Dehydrogenative Functionalization of Cyclopropylamides towards Allylic N,O-Acyl-acetal Derivatives

We disclose herein a novel photoredox and cobalt co-catalyzed ring-opening/acceptorless dehydrogenative functionalization of mono-donor cyclopropanes. This sustainable and atom-economic approach allows the rapid assembly of a wide range of allylic N,O-acyl-acetal derivatives. The starting materials are readily available and the reaction features mild conditions, broad substrate scope, and excellent functional group compatibility. The optimized conditions accommodate assorted cycloalkylamides and primary, secondary, and tertiary alcohols, with applications in late-stage functionalization of pharmaceutically relevant compounds, stimulating further utility in medicinal chemistry. Moreover, selective nucleophilic substitutions with various carbon nucleophiles were achieved in a one-pot fashion, offering a reliable avenue to access some cyclic and acyclic derivatives.

Photocatalytic (3 + 3) Annnulation of Vinyldiazo Compounds and Aminocyclopropanes

A (3 + 3) annulation of aminocyclopropanes and vinyldiazo compounds enabled by organo-photocatalysis is described. The reaction allows the regioselective synthesis of cyclohexenes bearing adjacent amino and carbonyl groups with broad functional group tolerance. In a departure from previous reports, our work demonstrated that a distonic radical cation can be preferentially intercepted by weakly nucleophilic vinyldiazo compounds, followed by an exclusive 6-endo radical cyclization for ring closure. Based on the interaction between adjacent amino and ester groups, the products can be further converted to cyclohexene-fused 1,3-oxazinane and azetidine.

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.

Aryl-, Akynyl-, and Alkenylbenziodoxoles: Synthesis and Synthetic Applications

Hypervalent iodine reagents are in high current demand due to their exceptional reactivity in oxidative transformations, as well as in diverse umpolung functionalization reactions. Cyclic hypervalent iodine compounds, known under the general name of benziodoxoles, possess improved thermal stability and synthetic versatility in comparison with their acyclic analogs. Aryl-, alkenyl-, and alkynylbenziodoxoles have recently received wide synthetic applications as efficient reagents for direct arylation, alkenylation, and alkynylation under mild reaction conditions, including transition metal-free conditions as well as photoredox and transition metal catalysis. Using these reagents, a plethora of valuable, hard-to-reach, and structurally diverse complex products can be synthesized by convenient procedures. The review covers the main aspects of the chemistry of benziodoxole-based aryl-, alkynyl-, and alkenyl- transfer reagents, including preparation and synthetic applications.

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.

Substrate-controlled C-H or C-C alkynylation of cyclopropanes: generation of aryl radical cations by direct light activation of hypervalent iodine reagents

We report the first oxidative C-H alkynylation of arylcyclopropanes. Irradiation of ethynylbenziodoxolone (EBX) reagents with visible light at 440 nm promoted the reaction. By the choice of the aryl group on the cyclopropane, it was possible to completely switch the outcome of the reaction from the alkynylation of the C-H bond to the oxyalkynylation of the C-C bond, which proceeded without the need for a catalyst, in contrast to previous works. The oxyalkynylation could also be extended to aminocyclopropanes as well as styrenes. Computations indicated that the C-H activation became a favoured nearly barrierless process in the presence of two ortho methyl groups on the benzene ring.

Progress in organocatalysis with hypervalent iodine catalysts

Hypervalent iodine compounds as environmentally friendly and relatively inexpensive reagents have properties similar to transition metals. They are employed as alternatives to transition metal catalysts in organic synthesis as mild, nontoxic, selective and recyclable catalytic reagents. Formation of C-N, C-O, C-S, C-F and C-C bonds can be seamlessly accomplished by hypervalent iodine catalysed oxidative functionalisations. The aim of this review is to highlight recent developments in the utilisation of iodine(III) and iodine(V) catalysts in the synthesis of a wide range of organic compounds including chiral catalysts for stereoselective synthesis. Polymer-, magnetic nanoparticle- and metal organic framework-supported hypervalent iodine catalysts are also described.

Activation of aminocyclopropanes via radical intermediates

Aminocyclopropanes are versatile building blocks for accessing high value-added nitrogen-containing products. To control ring-opening promoted by ring strain, the Lewis acid activation of donor-acceptor substituted systems is now well established. Over the last decade, alternative approaches have emerged proceeding via the formation of radical intermediates, alleviating the need for double activation of the cyclopropanes. This tutorial review summarizes key concepts and recent progress in ring-opening transformations of aminocyclopropanes via radical intermediates, divided into formal cycloadditions and 1,3-difunctionalizations.

1,3-Oxyalkynylation of Aryl Cyclopropanes with Ethylnylbenziodoxolones Using Photoredox Catalysis

Alkynes and cyclopropanes are vital motifs in chemistry. Herein, a photoredox catalyzed 1,3-oxyalkynylation of aryl cyclopropanes with ethylnylbenziodoxolones (EBXs) in an atom-economic fashion is described. This cascade comprises single-electron oxidation of the aryl cyclopropane and nucleophilic ring opening followed by radical alkynylation at the benzylic position. The EBX compounds act as bifunctional reagents providing the nucleophilic acid as well as the alkynyl entity. The introduced method features mild conditions and wide substrate scope.

Updates on hypervalent-iodine reagents in metal-free organic synthesis

Hypervalent iodine (HVI) chemistry is a rapidly growing subdomain of contemporary organic chemistry because of its enormous synthetic applications. The high nucleofugality of the phenyliodonio group (I+Ph) and their radical...

Photoinduced inverse Sonogashira coupling reaction

A transition-metal and photocatalyst-free, photoinduced inverse Sonogashira coupling reaction was developed. Under visible-light irradiation, the excited state iodoalkyne acted as an “alkynyl radical synthetic equivalent”.