De Novo Synthesis of 1,4-Dihydropyridines and Pyridines

Harnessing the Electrophilicity of Keteniminium Ions: A Simple and Straightforward Entry to Tetrahydropyridines and Piperidines from Ynamides

An efficient, modular and straightforward entry to tetrahydropyridines and piperidines is reported. This reaction is based on a formal intramolecular hydroalkylation of readily available, properly substituted ynamides which, upon simple activation under acidic conditions, generate highly reactive activated keteniminium ions whose reactivity can be finely controlled to induce a remarkably efficient [1,5]-hydride shift from unactivated C-H bonds and trigger a cationic cyclization which is complete within minutes.

TfOH-mediated [2 + 2 + 2] cycloadditions of ynamides with two discrete nitriles: synthesis of 4-aminopyrimidine derivatives

In this study, a concise and atom-economical TfOH-mediated [2 + 2 + 2] cycloaddition of ynamides with two discrete nitriles is developed to synthesize multi-substituted 4-aminopyrimidine.

Regioselective synthesis of 3,4-disubstituted isocoumarins through the Pd-catalyzed annulation of 2-iodoaromatic acids with ynamides

A Pd(0)-catalyzed annulation of 2-iodoaromatic acids with ynamides is described for the efficient synthesis of 3,4-disubstituted isocoumarins with excellent regioselectivities.

New page to access pyridine derivatives: synthesis from N-propargylamines

The pyridine is one of the simplest, yet most important N-heterocycles.

Copper-Mediated Cross-Dehydrogenative Coupling of 2-Methylpyridine and 8-Methylquinoline with Methyl Ketones and Benzamides

A synthetic method to prepare (E)-(pyridin-2-yl)enones and (E)-(quinolin-8-yl)enones that relies on the respective copper(I)-catalyzed formal cross-dehydrogenative coupling (CDC) reaction of 2-methylpyridine and 8-methylquinoline with methyl ketones has been discovered. The mechanism was delineated to follow a pathway involving oxidation of the N-heterocycle to its corresponding aldehyde adduct prior to reaction with the methyl ketone. The versatility and substrate dependent divergence in the reactivity of the copper-mediated CDC strategy was exemplified by its application to the synthesis of N-(quinolin-8-ylmethyl)amide and N-(quinolin-8-ylmethyl)aniline adducts on switching the cross-coupling partner to benzamides or an aniline derivative.

Synthesis of 3-Substituted 2-Aminochromones via Sn(IV)-Promoted Annulation of Ynamides with 2-Methoxyaroyl Chlorides

A Sn(IV)-promoted annulation reaction of ynamides is described for the efficient synthesis of 3-substituted 2-aminochromones under mild conditions. This novel method allows for a concomitant construction of C-C and C-O bonds between ynamides and 2-methoxyaroyl chlorides by a tandem Friedel-Crafts acylation/oxo-Michael addition/elimination strategy.

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.

Regioselective Synthesis of Highly Substituted Imidazoles via the Sequential Reaction of Allenyl Sulfonamides and Amines

A novel synthesis of imidazoles from electron-withdrawing group-substituted allenyl sulfonamides with amines was developed. The 4- and 5-functionalized imidazoles were constructed regioselectively, which depended on the substituents on the nitrogen atoms.

Ammonium iodide-promoted cyclization of ketones with DMSO and ammonium acetate for synthesis of substituted pyridines

A convenient and efficient method has been developed for the construction of substituted pyridines via ammonium iodide-promoted cyclization of ketones with DMSO and ammonium acetate, employing DMSO as the source of C4 or C6.

Transition-metal-free synthesis of substituted pyridines via ring expansion of 2-allyl-2H-azirines

A new strategy to open the 2-allyl-2H-azirines by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) promotion in metal-free conditions affording 1-azatrienes that in situ electrocyclize to the pyridines in good to excellent yields is reported. The reaction displays a broad substrate scope and good tolerance to a variety of substituents including aryl, alkyl, and heterocyclic groups. In addition, one-pot synthesis of pyridines from oximes via in situ formation of 2H-azirines was achieved.

Ynamides in ring forming transformations

The ynamide functional group activates carbon-carbontriple bonds through an attached nitrogen atom that bears an electron-withdrawing group. As a result, the alkyne has both electrophilic and nucleophilic properties. Through the selection of the electron-withdrawing group attached to nitrogen, chemists can modulate the electronic properties and reactivity of ynamides, making these groups versatile synthetic building blocks. The reactions of ynamides also lead directly to nitrogen-containing products, which provides access to important structural motifs found in natural products and molecules of medicinal interest. Therefore, researchers have invested increasing time and research in the chemistry of ynamides in recent years. This Account surveys and assesses new organic transforma-tions involving ynamides developed in our laboratory and in others around the world. We showcase the synthetic power of ynamides for rapid assembly of complex molecular structures. Among the recent reports of ynamide transformations, ring-forming reactions provide a powerful tool for generating molecular complexity quickly. In addition to their synthetic utility, such reactions are mechanistically interesting. Therefore, we focus primarily on the cyclization chemistry of ynamides. This Account highlights ynamide reactions that are useful in the rapid synthesis of cyclic and polycyclic structural manifolds. We discuss the mechanisms active in the ring formations and describe representative examples that demonstrate the scope of these reactions and provide mechanistic insights. In this discussion, we feature examples of ynamide reactions involving radical cyclizations, ring-closing metathesis, transition metal and non-transition metal mediated cyclizations, cycloaddition reactions, and rearrangements. The transformations presented rapidly introduce structural complexity and include nitrogen within or in close proximity to a newly formed ring (or rings). Thus, ynamides have emerged as powerful synthons for nitrogen-containing heterocycles and nitrogen-substituted rings, and we hope this Account will promote continued interest in the chemistry of ynamides.

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.

Metal-free synthesis of substituted pyridines from aldehydes and NH4OAc under air

A metal-free and efficient method for the synthesis of substituted pyridines with aldehydes and NH₄OAc under mild conditions using air as the oxidant was developed.

Turning unreactive copper acetylides into remarkably powerful and mild alkyne transfer reagents by oxidative umpolung

Upon oxidation, copper acetylides formally behave as highly electrophilic species that could be trapped by a wide range of nucleophiles.

Isothiourea-mediated one-pot synthesis of functionalized pyridines

Acids to bases: The synthesis of 2,4,6-trisubstituted pyridines from (phenylthio)acetic acid and a range of α,β-unsaturated ketimines is reported. This process proceeds by intermolecular Michael addition/lactamization, thiophenol elimination, and N- to O-sulfonyl migration, giving 2-sulfonate-substituted pyridines which are readily derivatized to generate structural diversity.