Aryl versus Alkyl Redox-Active Diazoacetates ─ Light-Induced C-H Insertion or 1,2-Rearrangement

Late-Stage Photoredox-Catalyzed Aryl C-H Bond Diazomethylation with Atomic Carbon Reagents

Herein, we present a novel class of diazo compounds as atomic carbon reagents substituted with two orthogonal redox-active leaving groups that were exploited in the late-stage construction of chiral centers with aryl C-H bonds from aromatic feedstocks and drug molecules. Key to the strategy was the use of photoredox catalysis to enable an initial C-H diazomethylation reaction able to generate diazomethyl-substituted redox-active esters. Subsequent construction of chiral centers with readily available starting materials proceeded using a broad range of well-known diazo and redox-active ester functionalizations. Moreover, the applicability of our novel atomic carbon reagent was tested in the automated parallel synthesis of a library of Fenofibrate derivatives.

Visible-Light-Promoted N-H Insertion/Controllable Transformation of Diazoalkanes and 3-Aminomethylated Maleimides

The utilization of photogenerated carbene species to perform N-H insertion reactions has attracted considerable attention in the past few years. In this Article, we disclose a visible-light-promoted N-H insertion of 3-aminomethylated maleimides with aryl diazoacetates under sole blue LED irradiation. Continuous flow reactor technology was exploited to improve the reaction efficiency. By simply varying the reaction conditions, the formed N-H insertion products could be selectively transferred to bioimportant octahydropyrrolo[3,4-c]pyrroles and E-selective trisubstituted olefins.

Photocatalytic Decarboxylative Functionalization of Cyclopropenes via Cyclopropenium Cation Intermediates

A photocatalytic decarboxylative functionalization of cyclopropenes is reported. Starting from a broad range of redox-active ester-substituted cyclopropenes, cyclopropenylphthalimides can be synthesized in the absence of a nucleophile. Alternatively, different carbon and heteroatom nucleophiles can be introduced. The transformation proceeds most probably through the formation of an aromatic cyclopropenium cation, followed by trapping with the nucleophiles.

Visible Light-Induced Reactions of Diazo Compounds and Their Precursors

In recent years, visible light-induced reactions of diazo compounds have attracted increasing attention in organic synthesis, leading to improvement of existing reactions, as well as to the discovery of unprecedented transformations. Thus, photochemical or photocatalytic generation of both carbenes and radicals provide milder tools toward these key intermediates for many valuable transformations. However, the vast majority of the transformations represent new reactivity modes of diazo compounds, which are achieved by the photochemical decomposition of diazo compounds and photoredox catalysis. In particular, the use of a redox-active photocatalysts opens the avenue to a plethora of radical reactions. The application of these methods to diazo compounds led to discovery of transformations inaccessible by the classical reactivity associated with carbenes and metal carbenes. In most cases, diazo compounds act as radical sources but can also serve as radical acceptors. Importantly, the described processes operate under mild, practical conditions. This Review describes this subfield of diazo compound chemistry, particularly focusing on recent advancements.

Visible photons as ideal reagents for the activation of coloured organic compounds

In recent decades, the traceless nature of visible photons has been exploited for the development of efficient synthetic strategies for the photoconversion of colourless compounds, namely, photocatalysis, chromophore activation, and the formation of an electron donor/acceptor (EDA) complex. However, the use of photoreactive coloured organic compounds is the optimal strategy to boost visible photons as ideal reagents in synthetic protocols. In view of such premises, the present review aims to provide its readership with a collection of recent photochemical strategies facilitated via direct light absorption by coloured molecules. The protocols have been classified and presented according to the nature of the intermediate/excited state achieved during the transformation.