Regioselective access to di- and trisubstituted pyridines via a metal-oxidant-solvent-free domino reaction involving 3-chloropropiophenones

A remarkable metal-oxidant-solvent- and base-free domino route for regioselective access to a wide range of 2,4-di- and 2,3,4/6-trisubstituted pyridines including carbo- and heterocyclic fused pyridines is reported. This [3C + 2C + 1N] cyclization reaction occurs between 3-chloropropiophenones (3C units), enolizable acyclic/cyclic ketones (2C sources) and NH₄OAc as a robust N source under neat conditions under an open atmosphere, producing new C=C and C=N-C bonds in highly chemo- and regioselective manners. Interestingly, this eco-friendly method has many positive features: excellent functional group tolerance, broad substrate scope, good to excellent regioselectivities, promising yields, no-unwanted products, neutral reaction conditions and appropriateness for large-scale synthesis. Mechanism studies reveal that the in situ generated β-amino ketone from 3-chloropropiophenone and an ammonium salt undergoes C=N bond formation with a ketone followed by an intramolecular cyclization process (C=C bond), which are the decisive steps for pyridine synthesis.

Tailor-made synthesis of fully alkylated/arylated nicotinates by FeCl3-mediated condensation of enamino esters with enones

A synthetic method for fully alkylated/arylated nicotinates was achieved by FeCl₃-mediated condensation of enamino esters and enones.

Facile Diversity-Oriented Synthesis of Polycyclic Pyridines and Their Cytotoxicity Effects in Human Cancer Cell Lines

A three-component cascade method has been developed for the direct synthesis of polysubstituted pyridines. This strategy provides a very convenient route to pyridines using a variety of β-bromo-α,β-unsaturated aldehydes, 1,3-diketones, and ammonium acetate without any additional catalyst or metal salt under mild conditions. A variety of β-ketoesters and 4-hydroxycoumarin were also used instead of 1,3-diketones for the diverse synthesis of polycyclic pyridines. One of the synthesized pyridines has been unambiguously established by a single crystal XRD study. All of the synthesized pyridine derivatives were evaluated for their antiproliferative properties in vitro against the human cancer cell lines HeLa, Me180, and ZR751. Compounds 4{4,1} and 4{2,4} showed significant cytotoxicity in the human breast cancer cell line ZR751 and cervical cancer cell line Me180, respectively, and a few other compounds were found to have moderate activities.

Expedient, catalyst-free, three-component synthesis of fused tetrahydropyridines in water

An expedient, three-component synthesis of oxazolo[3,2-a]pyridines and pyrido[2,1-b][1,3]oxazines was achieved under catalyst-free conditions in water.

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.