For more than 70 years, nitrogen-centered radicals have been recognized as potent synthetic intermediates. This review is a survey designed for use by chemists engaged in target-oriented synthesis. This review summarizes the recent paradigm shift in access to and application of N-centered radicals enabled by visible-light photocatalysis. This shift broadens and streamlines approaches to many small molecules because visible-light photocatalysis conditions are mild. Explicit attention is paid to innovative advances in N−X bonds as radical precursors, where X = Cl, N, S, O, and H. For clarity, key mechanistic data is noted, where available. Synthetic applications and limitations are summarized to illuminate the tremendous utility of photocatalytically generated nitrogen-centered radicals. CONTENTS 1. Introduction 2354 2. Nitrogen-centered Radicals Can Be Generated from Nitrogen−Chlorine Bonds in the Presence of Photoredox Catalysts 2357 3. Nitrogen-centered Radicals Can Be Generated from Nitrogen−Nitrogen Bonds within N-Aminopyridinium Salts in the Presence of Photoredox Catalysts 2359 4. Nitrogen-centered Radicals May Be Generated from Nitrogen−Sulfur Bonds 2363 5. Nitrogen-centered Radicals Can Be Generated from Nitrogen−Oxygen Bonds 2364 5.1. Iminyl Radicals Can Be Generated from O-Aryl and O-Acyl Oxime Analogues 2364 5.1.1.Radicals Prepared from O-Aryl or O-Acyl Oximes Can Add Across Olefins 2364 5.1.2. Radicals Prepared from O-Acyl Oximes Can Cyclize onto Arenes or Vinyl Arenes 2366 5.1.3. Radicals Prepared from O-Acyl Oximes Can Abstract Hydrogen Atoms 2367 5.2. Hydroxyacid-derived Oximes Are Appropriate Precursors to Iminyl Radicals 2368 5.2.1. These Iminyl Radicals Can Serve as Intermediates in Iminofunctionalization Reactions 2368 5.2.2. Hydroxyacid-derived Iminyl Radicals Can React with Chalcogens to Install New Chalcogen−Nitrogen Bonds 2370 5.3. Ketoximes and Aldoximes Can Serve as Precursors to Persistent Iminyl Radical Intermediates 2371 5.4. Iminyl Radicals That Are Generated from Strained Cyclic Oximes Can Engage in Ringopening Cascade Reactions 2374 5.4.1. These Ring-opening Cascades Are Wellestablished Strategies to Affect Distal Carbofunctionalization Reactions Involving Olefins 2374 5.4.2. By Using Hydroxyacid-derived Oxime Substrates, Ring-Opening Cascades Can Result in Direct Atom-or Group-transfer Processes 2375 5.4.3. Ring-opening Cascades Can Trigger Alkene Carbofunctionalization Reactions 2376 5.4.4. Ring-opening Cascades Can Be Intercepted by Transition-metal Mediated Bond-forming Processes 2378 5.4.5. Ring-opening Cascades Can Rely on O-Acyl Cyclic Oxime Substrates to Affect Alkene Carboetherification Reactions 2379

A facile preparation of arylmethyl and heteroarylmethyl phosphonate esters was achieved involving a Lewis acid mediated Michaelis-Arbuzov reaction at room temperature. Interaction of arylmethyl halides/alcohols with triethyl phosphite in the presence of Lewis acid at room temperature afforded phosphonate esters in good yields.

Stereogenic trifluoromethyl‐substituted carbon centers are highly sought‐after moieties in pharmaceutical and agrochemical discovery. Here, we show that lithiation–borylation reactions of 2‐trifluoromethyl oxirane give densely functionalized and highly versatile trifluoromethyl‐substituted α‐tertiary boronic esters. The intermediate boronate complexes undergo the desired 1,2‐rearrangement of the carbon‐based group with complete retentive stereospecificity, a process that was only observed in non‐polar solvents in the presence of TESOTf. Although the trifluoromethyl group adversely affects subsequent transformations of the α‐boryl group, Zweifel olefinations provide trifluoromethyl‐bearing quaternary stereocenters substituted with alkenes, alkynes and ketones.

One pot syntheses of substituted dibenzothiophene S,S-dioxides and fluorenones were successfully achieved by Diels-Alder reaction of benzo[c]furans with thiophene S,S-dioxides and indenones, respectively. Photophysical properties of representative seven- and nine-membered dibenzothiophene S,S-dioxide acenes were also reported.

An unprecedented oxidative cleavage of benzo[c]heterocycles using m‐CPBA is reported. The reaction of 1,3‐diaryl benzo[c]heterocycles with m‐CPBA (meta‐chloroperoxybenzoic acid) at room temperature for 5 min led to the formation of 1,2‐diaroylbenzenes in good to excellent yields.

A ZnBr(2)-mediated regioselective annulation of unsymmetrical 1,2-diarylmethinedipivalates in DCM at room temperature led to the formation of annulated arenes and heteroarenes. The annulation of the dipivalate proceeds through the intermediacy of benzylic carbocations followed by intramolecular cyclization and subsequent aromatization to give the annulated products. The annulation methodology is highly efficient for the syntheses of anthracene as well as naphtho[b]thiophene analogues.

An enantiodivergent method for the synthesis of multiply substituted allenes is described. Highly enantioenriched, point‐chiral boronic esters were synthesized by homologation of α‐seleno alkenyl boronic esters with lithiated carbamates and eliminated to form axially chiral allene products. By employing either oxidative or alkylative conditions, both syn and anti elimination could be achieved with complete stereospecificity. The process enables the synthesis of either M or P allenes from a single isomer of a point‐chiral precursor and can be employed for the enantioselective assembly of di‐, tri‐, and tetrasubstituted allenes.

A facile preparation of trans‐epoxides was achieved by a (EtO)3P–ZnBr2‐mediated deoxygenation reaction of the corresponding 2‐nitrobenzaldehydes. The sterically hindered analogues of 2‐nitrobenzaldehyde underwent a reaction with triethyl phosphite in the presence of ZnBr2 as the catalyst to form benzisoxazoles as the sole product. Under identical conditions, the reactions of electron‐rich as well as moderately electron‐deficient aryl aldehydes furnished the corresponding α‐hydroxy phosphonate esters.