Copper-Catalyzed Three-Component Carboamination of Arynes: Expeditious Synthesis of o-Alkynyl Anilines and o-Benzoxazolyl Anilines

Copper-catalysed electrophilic carboamination of terminal alkynes with benzyne looked at through the computational lens

A detailed computational mechanistic study of the copper-catalysed three-component-type electrophilic carboamination of terminal alkynes with benzyne and an archetypal O-benzoylhydroxylamine electrophile is presented. Probing various plausible pathways for relevant elementary steps and scrutinising performance degradation pathways, with the aid of a reliable computational protocol applied to a realistic catalyst model combined with kinetic analysis, identified the pathways preferably traversed in productive catalysis. It entails rapid alkynylcupration of in situ generated benzyne to deliver the arylcopper nucleophile that undergoes amination with the O-benzoylhydroxylamine electrophile to afford copper benzoate. Umpolung-enabled electrophilic amination favours a multistep SN2-type oxidative addition/N-C bond-forming reductive elimination sequence involving a short-lived formal {P^P}CuIII carboxylate amido aryl intermediate. SN2-type displacement of the benzoate leaving group at the arylcopper nucleophile, which represents the catalyst resting state, is predicted to be the turnover limiting step. Alkynolysis transforms copper benzoate back to catalytically competent alkynylcopper. The computational probe of a wider range of substrates reveals that only severely ring-strained C6-arynes, C6-cycloalkynes and electron-deficient cyclopropenes featuring a highly reactive C≡C linkage could replace benzyne. Moreover, strict control of stationary benzyne concentration is indispensable for electrophilic carboamination to ever become achievable.

Copper-Catalyzed Aryne Insertion into the Carbon-Iodine Bond of Heteroaryl Iodides

Aryne insertions into the carbon-iodine bond of heteroaryl iodides has been achieved for the first time. This novel reaction provides an efficient pathway for the synthesis of valuable building blocks 2-iodoheterobiaryls from heteroaryl iodides and o-silylaryl triflates in excellent regioselectivity. The copper(I) catalyst, which bears a N-heterocyclic carbene (NHC) ligand, is essential to accomplish the reaction. Control reactions and DFT calculations indicate that the coordination of copper, as a Lewis acid, with nitrogen atoms of heteroaryl iodides mediates the insertion of arynes into heteroaryl carbon-iodine bonds.

Hydroamination, Aminoboration, and Carboamination with Electrophilic Amination Reagents: Umpolung-Enabled Regio- and Stereoselective Synthesis of N-Containing Molecules from Alkenes and Alkynes

Nitrogen (N) is ubiquitously found in bioactive molecules, pharmaceutical agents, and organic functional materials. Accordingly, development of new C-N bond-forming catalysis has been one of the long-standing research subjects in synthetic organic chemistry. In this Perspective, recent advances in highly selective amination reactions with electrophilic amination reagents are described: by taking advantage of the concept of nitrogen umpolung, otherwise challenging aminofunctionalizations, such as hydroamination, aminoboration, and carboamination, of readily available feedstock-like alkenes and alkynes are possible, giving densely functionalized complex and often chiral alkylamines with high selectivity. The scope, limitations, and reaction mechanism are briefly summarized.

1,2-Difunctionalizations of alkynes entailing concomitant C–C and C–N bond-forming carboamination reactions

Vicinal carboamination of alkynes is a highly reliable and efficient practical strategy for the quick preparation of valuable and diverse amine derivatives starting from simple synthons. The last decade has witnessed numerous practical methods employing transition-metal-based/metal-free carboamination approaches using alkynes for the synthesis of these N-bearing entities. Driven by the renaissance of transition metal catalysis, intermolecular and intramolecular carboamination of alkynes comprising concomitant C–N and C–C bond formation has been studied extensively. In contrast to metal catalysis, though analogous metal-free approaches have been relatively less explored in the literature, they serve as alternatives to these expensive approaches. Despite this significant progress, reviews documenting such examples are sporadic; as a result, most reports of this type remained scattered throughout the literature, thereby hampering further developments in this escalating field. In this review, different conceptual approaches will be discussed and examples from the literature will be presented. Further, the reader will get insight into the mechanisms of different transformations.

The 1,2-difunctionalization of alkynes happening through concomitant C–C and C–N bond formation strategies have provide an unified access to diversely functionalized N-bearing heterocycles.

Synthesis of Oxazino[4,3-a]indoles and biological applications

This review brings together the various pathways to the oxazino[4,3-a]indole motif over the last decades. Representative examples showing the scope of these processes will illustrate the synthetic pathways and the biological activity of the synthesized oxazinoindoles will be mentioned wherever possible.

Palladium-Catalyzed Three-Component Coupling Reaction via Benzylpalladium Intermediate

Transition-metal catalyzed multi-component reactions have captured the attention of researchers in organic synthesis and drug synthesis due to their advantages of simple operation, easy availability of raw materials and without separation of intermediates. Among the multi-component reactions, the three-component processes have been developed into effective organic procedures. This personal account reviews our and other group's studies on the development of three-component coupling reaction for the rapid construction of two new chemical bonds simultaneously via benzylpalladium intermediates. Catalyst-switched three-component reactions of benzyl halides, activated olefins, and allyltributylstannane were successfully conducted to produce the corresponding benzylallylation products. Activation and conversion of carbon monoxide and carbon dioxide via π-benzylpalladium intermediates provide access to a wide range of unsaturated ketones and esters with excellent functional group tolerance. Meanwhile, other methods to produce benzylpalladium intermediates, including Heck insertion of alkenes into arylpalladium complexes, the oxidative addition of benzyl carbonate to palladium complexes and palladium-carbene migratory insertion, were also highlighted.

Palladium-Catalyzed Three-Component Carbocarbonation of Arynes: Expeditious Synthesis of o-Alkylated Arylacrylates and Stilbenes

A palladium-catalyzed multicomponent reaction involving olefin-tethered aryl iodides, arynes, and electrophilic alkenes has been developed for straightforward synthesis of o-alkylated arylacrylates and stilbenes through tandem intramolecular Heck cyclization/aryne dicarbofunctionalization.

Regioselective difunctionalization of pyridines via 3,4-pyridynes

A new regioselective 3,4-difunctionalization of 3-chloropyridines via 3,4-pyridyne intermediates is reported. Regioselective lithiation of 3-chloro-2-ethoxypyridine and a related 2-thio-derivative followed by treatment with aryl- and alkylmagnesium halides as well as magnesium thiolates at -78 °C produced 3,4-pyridynes during heating to 75 °C. Regioselective addition of the Grignard moiety in position 4 followed by an electrophilic quench in position 3 led to various 2,3,4-trisubstituted pyridines. This method was adapted into a continuous flow set-up. As an application, we have prepared a key intermediate for (±)-paroxetine.

Copper-catalyzed oxidative cyclization of glycine derivatives toward 2-substituted benzoxazoles

A novel and straightforward intramolecular cyclization of glycine derivatives to 2-substituted benzoxazoles through copper-catalyzed oxidative C-H/O-H cross-coupling was described. A variety of glycine derivatives involving short peptides underwent cross-dehydrogenative-coupling readily to afford diverse 2-substituted benzoxazoles. The synthetic method has the advantages of simple operation, broad substrate scope and mild reaction conditions, thus providing an alternative effective approach for benzoxazole construction.

Copper-catalysed three-component carboiodination of arynes: expeditious synthesis ofo-alkynyl aryl iodides

A copper-catalysed three-component reaction of arynes, terminal alkynes, and NIS provides an expeditious approach too-alkynyl aryl iodides.

Aerobic Cu-catalyzed oxidative 1 : 2 coupling of benzynes with terminal alkynes

Aryl-Cu(iii) may serve as an intermediate in Cu-catalyzed aerobic 1 : 2 couplings of arynes with terminal alkynes, allowing for one-step assemblies of arenediynes.