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

The present review offers an overview of the current approaches for the photochemical and photocatalytic generation of reactive intermediates and their application in the formation of carbon–carbon bonds. Valuable synthetic targets are accessible, including arylation processes, formation of both carbo- and heterocycles, alpha- and beta-functionalization of carbonyls, and addition reactions onto double and triple bonds. According to the recent advancements in the field of visible/solar light catalysis, a significant part of the literature reported herein involves radical ions and radicals as key intermediates, with particular attention to the most recent examples. Synthetic application of carbenes, biradicals/radical pairs and carbocations have been also reported.

Carbon-Carbon Bond Forming Reactions via Photogenerated Intermediates.

Visible-light photocatalysis is a rapidly developing and powerful strategy to initiate organic transformations, as it closely adheres to the tenants of green and sustainable chemistry. Generally, most visible-light-induced photochemical reactions occur through single-electron transfer (SET) pathways. Recently, visible-light-induced energy-transfer (EnT) reactions have received considerable attentions from the synthetic community as this strategy provides a distinct reaction pathway, and remarkable achievements have been made in this field. In this Review, we highlight the most recent advances in visible-light-induced EnT reactions.

Visible-Light-Induced Organic Photochemical Reactions through Energy-Transfer Pathways.

Transition metal-catalyzed C–H bond functionalizations have been the focus of intensive research over the last decades for the formation of C–C bonds from unfunctionalized arenes, heteroarenes, alkenes These direct transformations provide new approaches in synthesis with high atom- and step-economy compared to the traditional catalytic cross-coupling reactions However, such methods still suffer from several limitations including functional group tolerance and the lack of regioselectivity In addition, they often require harsh reaction conditions and some of them need the use of strong oxidant, in a stoichiometric amount, avoiding these processes to be truly eco-friendly The use of photoredox catalysis has contributed to a significant expansion of the scope of C(sp2)–H bond functionalizations which include the direct arylations, (perfluoro)alkylations, acylations, and even cyanations Most of these transformations involve the photochemical induced generation of a radical followed by its regioselective a

Photoredox Catalysis for Building C-C Bonds from C(sp2)-H Bonds.

The merger of photoredox catalysis with transition metal catalysis, termed metallaphotoredox catalysis, has become a mainstay in synthetic methodology over the past decade. Metallaphotoredox catalysis has combined the unparalleled capacity of transition metal catalysis for bond formation with the broad utility of photoinduced electron- and energy-transfer processes. Photocatalytic substrate activation has allowed the engagement of simple starting materials in metal-mediated bond-forming processes. Moreover, electron or energy transfer directly with key organometallic intermediates has provided novel activation modes entirely complementary to traditional catalytic platforms. This Review details and contextualizes the advancements in molecule construction brought forth by metallaphotocatalysis.

Metallaphotoredox: The Merger of Photoredox and Transition Metal Catalysis.

Bromodifluoromethylphosphonium bromide was solely used as the precursor of difluorocarbene. Herein, an unprecedented visible-light-induced hydrodifluoromethylation of alkenes with bromodifluoromethylphosphonium bromide using H2O and THF as hydrogen sources for the synthesis of difluoromethylated alkanes is described. This difluoromethylation is characterized by mild reaction conditions, ready availability of reagents, and excellent functional-group tolerance.

Visible-Light-Induced Hydrodifluoromethylation of Alkenes with a Bromodifluoromethylphosphonium Bromide.

Photoredox-Catalyzed Bromodifluoromethylation of Alkenes with (Difluoromethyl)triphenylphosphonium Bromide.

A process for tunable and chemo-, regio-, and stereoselective photocatalytic trifluoromethylation of styrenes was developed. Thermodynamically stable E-trifluoromethylated alkenes were prepared using Togni’s reagent in the presence of Ru(bpy)3Cl2·6H2O under visible light irradiation, whereas less thermodynamically stable Z-trifluoromethylated alkenes were obtained by employing Umemoto’s reagent and photocatalyst Ir(ppy)3.

Chemo-, Regio-, and Stereoselective Trifluoromethylation of Styrenes via Visible Light-Driven Single-Electron Transfer (SET) and Triplet–Triplet Energy Transfer (TTET) Processes

A convenient, visible light induced oxidifluoromethylation of styrenes was developed. This protocol employs the readily prepared difluoromethyltriphenylphosphonium bromide as the difluoromethylating reagent and alcohols/water as the nucleophiles, affording difluoromethyl(CF2H)-containing alcohols and ethers in moderate to excellent yields.

Visible Light Induced Oxydifluoromethylation of Styrenes with Difluoromethyltriphenylphosphonium Bromide

A mild and versatile approach for the direct introduction of ethoxycarbonyldifluoromethyl-group to heteroarenes via visible-light photocatalysis has been developed. The new photoredox protocol has enabled the difluoromethylenation of heteroarenes containi

Qing-Yu Lin

Papers

Visible-Light-Induced Hydrodifluoromethylation of Alkenes with a Bromodifluoromethylphosphonium Bromide.

Photoredox-Catalyzed Bromodifluoromethylation of Alkenes with (Difluoromethyl)triphenylphosphonium Bromide.

Chemo-, Regio-, and Stereoselective Trifluoromethylation of Styrenes via Visible Light-Driven Single-Electron Transfer (SET) and Triplet–Triplet Energy Transfer (TTET) Processes

Visible Light Induced Oxydifluoromethylation of Styrenes with Difluoromethyltriphenylphosphonium Bromide

Direct Introduction of Ethoxycarbonyldifluoromethyl-Group to Heteroarenes with Ethyl Bromodifluoroacetate via Visible-Light Photocatalysis