Photoredox-Catalyzed Strain-Release-Driven Synthesis of Functionalized Spirocyclobutyl Oxindoles

Spirocyclobutyl oxindoles have garnered substantial attention in drug discovery and pharmaceuticals owing to their wide range of biological activities. Strain-release in small-ring compounds is a powerful strategy to enable efficient access to complex molecules. In this study, we successfully realized a photoredox-catalyzed strain-release radical spirocyclization approach to attain functionalized spirocyclobutyl oxindoles. A diverse array of radicals, such as sulfonyl, phosphonyl, and trifluoromethyl, were added efficiently to the strained C-C σ-bond of bicyclobutanes (BCBs) to afford a library of spirocyclobutyl oxindoles. Furthermore, the obtained products could be transformed into valuable building blocks. The observed reactivity and selectivity have been rationalized based on density functional theory calculations.

Photo-induced phosphorylation/cyclization of N-homoallyl and N-allyl aldehyde hydrazones to access phosphorylated tetrahydropyridazines and dihydropyrazoles

A photocatalytic radical carbophosphorylation/cyclization of N-homoallyl aldehyde hydrazones with phosphine oxides was developed under metal-free conditions, achieving phosphorylated tetrahydropyridazines in yields up to 95%. Phosphorylated dihydropyrazoles were also constructed, by reacting N-allyl aldehyde hydrazones with phosphine oxides under the same conditions.

Synthesis of γ-Oxo-phosphonates via N-Heterocyclic Carbene-Catalyzed Acylphosphorylation of Alkenes

In this study, we present an N-heterocyclic carbene-catalyzed method for the radical acylphosphorylation of alkenes. Electrochemical investigations were employed to identify an appropriate class of oxime phosphonates capable of undergoing a single-electron transfer (SET) with Breslow enolates. The resulting phosphoryl radicals were effectively coupled with diverse styrenes and aldehydes to yield a variety of γ-oxo-phosphonates. Both radical clock experiments and electrochemical studies support our reaction design, and a plausible mechanism for the organocatalytic transformation is proposed.

Iron-Catalyzed Csp2-Csp3 Cross-Coupling via Double Decarboxylation: One Step Synthesis of Remote Polar Alkenes

Herein, we report an efficient photoinduced iron-catalyzed strategy for cross-couplings of alkyl carboxylic and acrylic acids, which provides a powerful tool for the synthesis of a variety of alkenes with polar functional groups. This novel synthetic methodology can also be applied to the preparation of ketones by using α-keto acids. Mechanistic experiments revealed preliminary mechanistic details. Diverse functionalization could be achieved, which may help streamline the synthesis of complex analogues for drug discovery.

Visible-Light-Promoted Phosphorylation/Cyclization of 1-Acryloyl-2-cyanoindoles in Green Solvent

A visible-light-induced persulfate-promoted cascade phosphorylation/cyclization reaction to access various phosphorylated pyrrolo[1,2-a]indolediones under mild conditions was developed. Notably, the transformation was carried out with diethyl carbonate/H₂O as a green medium at room temperature. More impressively, traditional metal catalysts and photocatalysts could be effectively avoided. The reactions are simple to operate, easy to scale up, and have good functional group tolerance.

Visible-light-facilitated P-center radical addition to C[double bond, length as m-dash]X (X = C, N) bonds results in cyclizations

Visible-light-facilitated phosphorus radical reactions have been developed as a powerful and sustainable tool for the synthesis of various organophosphorus compounds. In general, these reactions require stoichiometric amounts of oxidants, and reductants, bases, and radical initiators, leading to uneconomical and complicated processes. Progress has been made over the past few years toward using reactions that proceed under eco-benign and mild reaction conditions. Furthermore, these reactions have broad functional group tolerance, with some facile and economical pathways. Herein, we summarize the discoveries and achievements pertaining to C-P bond formation through a visible light photocatalysis procedure with high atom economy, made by our group and other research groups. It was established that greener and more environmentally friendly approaches do not require an additional oxidant or base. Moreover, we have designed and synthesized a new type of P-radical precursor, which can take part in reactions without the requirement for any additional bases, oxidants, and additives. This breakthrough, pertaining to novel visible-light-induced transformations, will be discussed and a plausible mechanism is proposed, based on corresponding experiments and the literature.

Shining Light on the Light-Bearing Element: A Brief Review of Photomediated C–H Phosphorylation Reactions

Organophosphorus compounds have numerous useful applications, from versatile ligands and nucleophiles in the case of trivalent organophosphorus species to therapeutics, agrochemicals and material additives for pentavalent species. Although phosphorus chemistry is a fairly mature field, the construction of C–P(V) bonds relies heavily on either prefunctionalized substrates such as alkyl or aryl halides, or requires previously oxidized bonds such as C=N or C=O, leading to potential sustainability issues when looking at the overall synthetic route. In light of the recent advances in photochemistry, using photons as a reagent can provide better alternatives for phosphorylations by unlocking radical mechanisms and providing interesting redox pathways. This review will showcase the different photomediated phosphorylation procedures available for converting C–H bonds into C–P(V) bonds.

1 Introduction

1.1 Organophosphorus Compounds

1.2 Phosphorylation: Construction of C–P(V) Bonds

1.3 Photochemistry as an Alternative to Classical Phosphorylations

2 Ionic Mechanisms Involving Nucleophilic Additions

3 Mechanisms Involving Radical Intermediates

3.1 Mechanisms Involving Reactive Carbon Radicals

3.2 Mechanisms Involving Phosphorus Radicals

3.2.1 Photoredox: Direct Creation of Phosphorus Radicals

3.2.2 Photoredox: Indirect Creation of Phosphorus Radicals

3.2.3 Dual Catalysis

3.3 Photolytic Cleavage

4 Conclusion and Outlook

Visible light-mediated CP bond formation reactions

Organophosphorus compounds have attracted continuous attention in materials science, agrochemical and pharmaceutical fields due to their unique bioactivities. Thus, the development of novel and robust manners for the construction new CP bond has therefore gained great interests in synthetic organic chemistry. Because of their intrinsic sustainability and green chemistry character, visible light-induced photoredox catalysis has been widely applied in the construction of new chemical bonds, including the formation of CP bond. In this review, we summarized recent achievements in CP bond formation reactions initiated by visible light-induced photoredox catalysis, which mainly focusing on the discussion of reaction design and the mechanism.