Synthesis of Substituted Pyridines from Cascade [1 + 5] Cycloaddition of Isonitriles to N-Formylmethyl-Substituted Enamides, Aerobic Oxidative Aromatization, and Acyl Transfer Reaction

Synthesis of Oxazolidin-2-ones by Oxidative Coupling of Isonitriles, Phenyl Vinyl Selenone, and Water

Reaction of alkyl isocyanides, phenyl vinyl selenone, and water in the presence of a catalytic amount of Cs2 CO3 afforded oxazolidin-2-ones in good yields. This unprecedented heteroannulation process created four chemical bonds in a single operation with the isocyano group acting formally as a polarized double bond and phenyl vinyl selenone as a latent 1,3-dipole. The phenylselenonyl group played a triple role as an electron-withdrawing group to activate the 1,4-addition, a leaving group, and a latent oxidant in this transformation.

Facile synthesis of heavily-substituted alkynylpyridines via a Sonogashira approach

A robust synthesis of highly-substituted alkynylpyridines via a Sonogashira approach is described, providing a library of functionalized pyridines for biological studies.

Copper-catalyzed alkylarylation of activated alkenes using isocyanides as the alkyl source: an efficient radical access to 3,3-dialkylated oxindoles

A novel copper-catalyzed oxidative cyclization of N-arylacrylamides for the synthesis of 3,3-dialkylated oxindoles is described using isocyanides as alkyl radical precursors.

Isocyanide-Based Multicomponent Reactions for the Synthesis of Heterocycles

Multicomponent reactions (MCRs) are extremely popular owing to their facile execution, high atom-efficiency and the high diversity of products. MCRs can be used to access various heterocycles and highly functionalized scaffolds, and thus have been invaluable tools in total synthesis, drug discovery and bioconjugation. Traditional isocyanide-based MCRs utilize an external nucleophile attacking the reactive nitrilium ion, the key intermediate formed in the reaction of the imine and the isocyanide. However, when reactants with multiple nucleophilic groups (bisfunctional reactants) are used in the MCR, the nitrilium intermediate can be trapped by an intramolecular nucleophilic attack to form various heterocycles. The implications of nitrilium trapping along with widely applied conventional isocyanide-based MCRs in drug design are discussed in this review.

Exploring tertiary enamides as versatile synthons in organic synthesis

Tertiary enamides have long been thought of as stable and marginally valuable enamine variants in synthesis. This notion has been challenged, however, in recent years. Enabling the regulation of the cross-conjugation system of the tertiary enamides has been successfully shown to enhance delocalization of the nitrogen lone-pair electrons into a carbon-carbon double, thereby reinvigorating the enaminic reactivity of the tertiary enamides. In this article, I summarize the recent advances in the exploration of the nucleophilic reactions of tertiary enamides and their applications in the synthesis of natural products and heterocyclic compounds of biological and pharmaceutical relevance, with a primary focus on our own work.

Silver-Catalyzed Cross-Coupling of Isocyanides and Active Methylene Compounds by a Radical Process

Isocyanides are versatile building blocks, and have been extensively exploited in C-H functionalization reactions. However, transition-metal-catalyzed direct C-H functionalization reactions with isocyanides suffer from over-insertion of isocyanides. Reported herein is a radical coupling/isomerization strategy for the cross-coupling of isocyanides with active methylene compounds through silver-catalysis. The method solves the over-insertion issue and affords a variety of otherwise difficult to synthesize β-aminoenones and tricarbonylmethanes under base- and ligand-free conditions. This report presents a new fundamental C-C bond-forming reaction of two basic chemicals.

Base-Promoted N-Pyridylation of Heteroarenes Using N-Propargyl Enaminones as Equivalents of Pyridine Scaffolds

N-Pyridylation of various N-heteroarenes, including N-heteroarene-containing peptides, was achieved using N-propargyl enaminones (isolated or generated in situ from propargyl amine and propynones) as masked polysubstituted pyridine cores. This metal-free procedure proceeds under mild reaction conditions and generates 1 equiv of H2O as the sole byproduct.

Multicomponent synthesis of pyridines via diamine functionalized mesoporous ZrO2 domino intramolecular tandem Michael type addition

A new and straightforward synthetic method was developed for the facile synthesis of heterocycle-fused pyridine derivatives in aqueous media from Knoevenagel condensation between an aromatic aldehyde and an active methylene compound.

Synthesis of Passerini adducts from aldehydes and isocyanides under the auxiliary of water

An efficient protocol for the synthesis of the Passerini adducts α-acyloxycarboxamides from aldehydes, isocyanides and water in a molecular ratio of 3 : 1 : 3 was described.

N-Substitution dependent stereoselectivity switch in palladium catalyzed hydroalkynylation of ynamides: a regio and stereoselective synthesis of ynenamides

A palladium catalysed regioselective hydroalkynylation of ynamides for ynenamides is achieved with an N-substitution dependent stereoselectivity switch.

Organocatalyzed oxidative N-annulation for diverse and polyfunctionalized pyridines

A variety of polyfunctionalized pyridines were synthesized from readily available ketones with α,β-unsaturated aldehydes and ammonium acetate under a mild organocatalyst.

Silver(i)–N-heterocyclic carbene catalyzed multicomponent reactions: a facile synthesis of multisubstituted pyridines

A room temperature four component reaction between aromatic aldehydes, CH₂(CN)₂and NH₄OAc with ketones mediated by Ag(i)–NHC pre-catalysts to produce multisubstituted pyridines in a short reaction time in eco-friendly ethanol was described.

Synthesis of diverse nitrogen-enriched heterocyclic scaffolds using a suite of tunable one-pot multicomponent reactions

Five elegant and switchable three-component reactions which enable access to a new series of nitrogen-containing heterocycles are reported. A novel one-step addition of an isocyanide to a hydrazine derived Schiff base affords unique six-membered pyridotriazine scaffolds (A and E). With slight modification of reaction conditions and replacement of the nucleophilic isocyanide moiety with different electrophiles (i.e., isocyanates, isothiocyanates, cyclic anhydrides, and acyl chlorides) five-membered triazolopyridine scaffolds (B, D, F, G) are generated in a single step. Furthermore, the use of phenyl hydrazine enables access to dihydroindazole-carboxamides, devoid of a bridge-head nitrogen (C). All protocols are robust and tolerate a diverse collection of reactants, and as such, it is expected that the new scaffolds and associated chemistry will garner high interest from medicinal chemists involved in either file enhancement or specific target-related drug discovery campaigns.

Three-component coupling approach for the synthesis of diverse heterocycles utilizing reactive nitrilium trapping

The formation of an unexpected heterocyclic scaffold, a benzoxazole, in a three-component reaction between a ketone, isocyanide, and 2-aminophenol was encountered. This reaction involved a benzo[b][1,4]oxazine intermediate resulting from intramolecular attack of the aminophenol hydroxyl group on the nitrilium ion. Unlike previous literature examples, the trapped nitrilium benzo[b][1,4]oxazine could readily be subjected to ring opening with bis-nucleophiles. The reaction scope includes simple linear as well as complex cyclic ketones and substituted 2-aminophenols. A representative benzoxazole product could be further diversified to yield drug-like compounds.

Rh(III)-catalyzed decarboxylative coupling of acrylic acids with unsaturated oxime esters: carboxylic acids serve as traceless activators

α,β-Unsaturated carboxylic acids undergo Rh(III)-catalyzed decarboxylative coupling with α,β-unsaturated O-pivaloyl oximes to provide substituted pyridines in good yield. The carboxylic acid, which is removed by decarboxylation, serves as a traceless activating group, giving 5-substituted pyridines with very high levels of regioselectivity. Mechanistic studies rule out a picolinic acid intermediate, and an isolable rhodium complex sheds further light on the reaction mechanism.

A catalyst-controlled selective synthesis of pyridines and pyrroles

We have developed a dual reaction manifold that enables the selective synthesis of both pyridines and pyrroles from the common substrates α-diazo oxime ethers.

Functionalized imidazoliniums from the three-component domino reaction of N-formylmethylcarboxamides with amines and isocyanides

Functionalized imidazoliniums were synthesized efficiently from the three-component domino reaction of N-formylmethyl-substituted tertiary amides and enamides with amines and isocyanides.

A heavy metal- and oxidant-free, one-pot synthesis of pyridines and fused pyridines based on a Lewis acid-catalyzed multicomponent reaction

Pyridines and fused pyridines are accessible by a combination of a Lewis acid-catalyzed multicomponent reaction and aromatization involving loss of a 2-furylmethyl chain.

A new approach to pyridines through the reactions of methyl ketones with 1,2,4-triazines

A new route to prepare pyridine derivatives based on inverse electron demand Diels–Alder/retro-Diels–Alder reactions of ketones with 1,2,4-triazines is reported, which is complementary to the classical Boger reaction.

Direct alkenyl C–H functionalization of cyclic enamines with carboxylic acids via Rh catalysis assisted by hydrogen bonding

Enamines and enamides are important synthetic intermediates.