Nickel-Catalyzed β-Regioselective Amination/Cyclization of Ynamide-Nitriles with Amines: Synthesis of Functionalized 3-Aminoindoles and 4-Aminoisoquinolines

A Cascade Synthesis of Furo-Pyrrolo-Pyridines via Pd(II)-Catalyzed Dual N-H/C Annulative-Cyclization

A Pd(II)-catalyzed non-template synthesis of furo[2,3-b]pyrrolo[2,3-d]pyridines from β-ketodinitriles and buta-1,3-diynes has been accomplished via dual annulative cyclization. The participation of both the nitrile (-CN) groups led to the concurrent construction of three heterocycles viz. furan, pyrrole, and pyridine forming C-C, C=C, C-O, C-N, and C=N bonds in one pot. The synthetic utility of the protocol was further demonstrated through a few post-synthetic manipulations.

Intermolecular 1,2-Difunctionalization of Nitriles via Redox Gold Catalysis: Synthesis of Benzoxazoles and Benzimidazoles

The unprecedent gold-catalyzed intermolecular 1,2-difunctionalization of nitriles with o-iodophenols or o-iodoanilines via Au(I)/Au(III) redox catalysis has been developed, providing an expedient route to the synthesis of benzoxazoles or benzimidazoles with broad substrate scope and high functional compatibility. Mechanistic investigation reveals that the Au(III)-Ar species generated via oxidative addition of o-iodophenol to MeDalphosAu+, serves as a key intermediate. Particularly, this annulation is initiated by oxidative addition, rather than the nucleophilic attack of the phenol moiety in o-iodophenol towards the nitrile. The method was also applied to the synthesis of poly aza-heterocycles via a cascade Au(I)/Au(III) and Au(I) catalysis relay.

Access to 2,3-Dihydropyridines Involving Cyano Transformation Relay through Gold Catalysis Assisted by a Lewis Acid

A gold(I)-catalyzed cyclization of enynone-nitriles with amines to 2,3-DHPs assisted by La(OTf)3 has been developed. The compatibility with abundant nucleophiles, high functional group tolerance, rapid assembly of molecular complexity, and late-stage functionalization of bioactive substances make this approach attractive for the construction of 2,3-DHPs, which have rarely been synthesized in the literature. The reaction proceeds via cascade cyclization involving gold/Lewis acid cooperative activation of the alkene and the cyano moiety.

PPh3-Mediated Cascade Reaction of 2-Alkynylnitrobenzenes and Thioureas for the Construction of Imidazo[4,5-b]indole-2-thiones

A simple method for the preparation of imidazo[4,5-b]indole-2-thiones from 2-alkynylnitrobenzenes and thioureas is described. In the reaction, a Wittig-like process was triggered by PPh₃ and followed by a cyclization step. The products were afforded in yields of 70-98% under mild conditions. Additionally, the 2-alkynylnitrobenzenes were stable and could be prepared via a simple coupling step.

Nickel-catalyzed asymmetric reductive arylcyanation of alkenes with acetonitrile as the cyano source

Chiral 3-cyanomethyl oxindoles were synthesized in high enantioselectivities and yields. The employment of acetonitrile as a cyano source via Zn(OTf)2-assisted β-carbon elimination is distinct from the common cyanation reaction modes.

Diverse reactivity of alkynes in C-H activation reactions

Alkynes occupy a prominent role as a coupling partner in the transition metal-catalysed directed C-H activation reactions. Due to low steric requirements and linear geometry, alkynes can effectively coordinate with metal d-orbitals. This makes alkynes one of the most successful coupling partners in terms of the number of useful transformations. Remarkably, by changing the reaction conditions and transition-metals from 5d to 3d, the pattern of reactivity of alkynes also changes. Due to the varied reactivity of alkynes, such as alkenylation, annulation, alkylation, and alkynylation, they have been extensively used for the synthesis of valuable organic molecules. Despite enormous explorations with alkynes, there are still a lot more possible ways by which they can be made to react with M-C bonds generated through C-H activation. Practically there is no limit for the creative use of this approach. In particular with the development of new high and low valent first-row metal catalysts, there is plenty of scope for this chemistry to evolve as one of the most explored areas of research in the coming years. Therefore, a highlight article about alkynes is both timely and useful for synthetic chemists working in this area. Herein, we have highlighted the diverse reactivity of alkynes with various transition metals (Ir, Rh, Ru, Pd, Mn, Fe, Co, Ni, Cu) and their applications, along with some of our thoughts on future prospects.

Synergetic copper/zinc catalysis: synthesis of aryl/heteroaryl-fused 1H-pyrrolo[3,2-c]pyridines

Scaffolds having a 1H-pyrrolo[3,2-c]pyridine core show significant biological activity. Herein, we report a synergetic copper/zinc-catalyzed one-step annulation reaction of 2-amino (hetero)arylnitriles with ynamide-derived buta-1,3-diynes to deliver 1H-pyrrolo[3,2-c]quinoline-2,4-diamine derivatives in moderate to good yields. The annulation reaction follows a double cyclization pathway. The gram-scale synthesis of 1H-pyrrolo[3,2-c]quinoline-2,4-diamine proves the practicality of this protocol.

Synthesis of ortho-Diamino-Functionalized 1-Arylnaphthalenes through Nickel-Catalyzed Cyclization of Ynamide-Benzylnitriles with Organoboronic Acids

A nickel-catalyzed highly regioselective addition/cyclization of ynamide-benzylnitriles with organoboronic acids has been developed. The reaction offers an attractive route for the construction of diamino-functionalized 1-arylnaphthalenes, which is difficult to synthesize by other methods. In addition, a wide range of functional groups are tolerated in this reaction.

Photoinduced oxidative cyclopropanation of ene-ynamides: synthesis of 3-aza[n.1.0]bicycles via vinyl radicals

The first photoinduced synthesis of polyfunctionalized 3-aza[n.1.0]bicycles from readily available ene-ynamides and 2,6-lutidine N-oxide using an organic acridinium photocatalyst is reported. Applying a photocatalytic strategy to the reactive distonic cation vinyl radical intermediate from ynamide, a series of bio-valuable 3-azabicycles, including diverse 3-azabicyclio[4.1.0]heptanes and 3-azabicyclo[5.1.0]octanes that are challenging to accomplish using traditional methods, have been successfully synthesized in good to high yields under mild and metal-free conditions. Mechanistic studies are consistent with the photocatalyzed single-electron oxidation of ene-ynamide and the intermediacy of a putative cationic vinyl radical in this transformation. Importantly, this strategy provides new access to the development of photocatalytic vinyl radical cascades for the synthesis of structurally sophisticated substrates.

Nonmetal-catalyzed hydroamination of ynamides with amines

A TfOH-catalyzed hydroamination of ynamides with primary and secondary amines under mild reaction conditions is described for the efficient synthesis of N-arylimines and ethene-1,1-diamines.