The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C–C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of...

Advances in Synthetic Applications of Hypervalent Iodine Compounds

10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

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).

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

Carbon trifluoromethylation reactions of hydrocarbon derivatives and heteroarenes.

Nucleophilic phosphine catalysis has proven to be a powerful tool in organic synthesis, which can provide easy access to cyclic, bicyclic or polycyclic carbocycles and heterocycles. Owing to their comparatively strong and readily tunable nucleophilicity, phosphines can be easily tailored to efficient annulation reactions with good control over reaction selectivity. This has resulted in a tremendous increase in their scope and in a concomitant number of reports where phosphine-triggered annulation reactions occur. This tutorial review summarizes the recent achievements in this area.

Phosphine-triggered synthesis of functionalized cyclic compounds

Herein, we report a method for iron-catalyzed, visible-light-induced hydrosilylation reactions of electron-deficient alkenes to produce value-added silicon compounds. Alkenes bearing functional groups with different steric properties were suitable substrates, as were derivatives of structurally complex natural products. Mechanistic studies showed that chlorine radicals generated by iron-catalyzed ligand-to-metal charge transfer in the presence of lithium chloride promoted the formation of silyl radicals.Introduction.

Visible-Light-Induced Hydrosilylation of Electron-deficient Alkenes by Iron Catalysis.

Rh(III)-catalyzed C8 arylation of quinoline N-oxides with arylboronic acids

(−)-Gossypol displayed an obviously higher antiviral activity against the tobacco mosaic virus (TMV) than (+)-gossypol, whereas the anti-TMV activity of (−)-gossypol Schiff bases is not significantly higher than (+)-gossypol Schiff bases. A mechanism study indicated that these gossypol compounds could neither inhibit the multiplication of TMV nor induce the systemic acquired resistance of tobacco plants. However, gossypol compounds with high anti-TMV activities could induce the accumulation of reactive oxygen species (ROS) in tobacco leaves, and this result is in accordance with the characteristics of extreme resistance featuring a necessary early and rapid ROS (O2˙− or H2O2) accumulation in plants. Further study showed that, the anti-TMV activities of the test compounds decreased synchronously when the O2˙− accumulation was reduced by superoxide dismutase (SOD). However, when the H2O2 accumulation was suppressed by hydrogen peroxidase (CAT), the anti-TMV activities did not change. Therefore, compared with the H2O2 accumulation in gossypol compounds-treated tobacco leaves, the O2˙− accumulation is a key factor for the development of the anti-TMV activities of those compounds, and their anti-TMV mechanism belonged to their extreme resistance. Further study showed that the O2˙− accumulation in the (−)-gossypol-treated tobacco leaves was mainly from the tobacco itself, whereas the same O2˙− accumulation in the gossypol Schiff base-treated tobacco leaves was at least partially related to the O2˙− produced by the compound. Accordingly, gossypol compounds achieved their anti-TMV activities by stimulating O2˙− accumulation in the tobacco, which was induced either by the O2˙− production or by the chirality of the gossypol compounds, and this result could also explain why (−)-gossypol or gossypol Schiff bases displayed higher anti-TMV activities than (+)-gossypol.

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Antiviral activity and mechanism of gossypols: effects of the O2˙− production rate and the chirality

Herein, we describe a convenient general protocol for monofluoroalkenylation reactions of alkyl bromides involving cooperative visible-light photoredox catalysis and halogen abstraction. Mechanistic experiments showed that the products were generated by selective cross-coupling of aliphatic radicals with fluoroalkenyl radicals. Silyl radical-mediated halogen abstraction enabled the protocol to be used for the monofluoroalkenylation of a broad range of alkyl and heteroaryl halides. The protocol could be carried out on a gram scale and was applied to cholesterol, indicating its utility for late-stage monofluoroalkenylation reactions.

Dehalogenative Cross-Coupling of gem-Difluoroalkenes with Alkyl Halides via a Silyl Radical-Mediated Process.

Due to widespread drug resistance in parasitic nematodes, there is a need to develop new anthelmintics. Given the cost and time involved in developing a new drug, the repurposing of known chemicals can be a promising, alternative approach. In this context, we tested a library (n = 600) of natural product-inspired pesticide analogues against exsheathed third stage-larvae (xL3s) of Haemonchus contortus (barber's pole worm) using a whole-organism, phenotypic screening technique that measures the inhibition of motility and development in treated larvae. In the primary screen, we identified 32 active analogues derived from chemical scaffolds of arylpyrrole or fipronil. The seven most promising compounds, selected based on their anthelmintic activity and/or limited cytotoxicity, are arylpyrroles that reduced the motility of fourth-stage larvae (L4s) with significant potency (IC50 values ranged from 0.04 ± 0.01 μM to 4.25 ± 0.82 μM, and selectivity indices ranged from 10.6 to 412.5). Since the parent structures of the active compounds are uncouplers of oxidative phosphorylation, we tested the effect of selected analogues on oxygen consumption in xL3s using the Seahorse XF24 flux analyser. Larvae treated with the test compounds showed a significant increase in oxygen consumption compared with the untreated control, demonstrating their uncoupling activity. Overall, the results of the present study have identified natural product-derived molecules that are worth considering for chemical optimisation as anthelmintic drug leads.

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Yuxiu Liu

Papers

Visible-Light-Induced Hydrosilylation of Electron-deficient Alkenes by Iron Catalysis.

Rh(III)-catalyzed C8 arylation of quinoline N-oxides with arylboronic acids

Antiviral activity and mechanism of gossypols: effects of the O2˙− production rate and the chirality

Dehalogenative Cross-Coupling of gem-Difluoroalkenes with Alkyl Halides via a Silyl Radical-Mediated Process.

Arylpyrrole and fipronil analogues that inhibit the motility and/or development of Haemonchus contortus in vitro.