Synthesis of 2-(hetero)arylthieno[2,3-b] or [3,2-b]pyridines from 2,3-dihalopyridines, (hetero)arylalkynes, and Na2S. Further functionalizations

Access to Thienopyridine and Thienoquinoline Derivatives via Site-Selective C-H Bond Functionalization and Annulation

To develop of an effective synthetic methodology for biologically relevant thienopyridines, a concise and efficient protocol is described for the synthesis of a series of substituted thienopyridine and thienoquinoline derivatives with high selectivity using EtOCS₂K as the sulfur source. The reaction proceeds via metal-free, site-selective C-H bond thiolation and cyclization of the alkynylpyridine and alkynylquinoline substrates.

Unusual Oxidative Dimerization in the 3-Aminothieno[2,3-b]pyridine-2-carboxamide Series

Noncatalyzed, regio- and stereoselective hypochlorite oxidation of 3-aminothieno[2,3-b]pyridine-2-carboxamides is presented. Unexpectedly, the oxidation proceeded by different mechanistic pathways, and different products were formed, depending on the nature of solvents used. A possible mechanism, the structure of products, kinetics and dynamics of intramolecular processes, and biological activity of products are discussed.

Synthesis of 2-Organylchalcogenopheno[2,3-b]pyridines from Elemental Chalcogen and NaBH4 /PEG-400 as a Reducing System: Antioxidant and Antinociceptive Properties

An alternative method to prepare 2-organylchalcogenopheno[2,3-b]pyridines was developed by the insertion of chalcogen species (selenium, sulfur or tellurium), generated in situ, into 2-chloro-3-(organylethynyl)pyridines by using the NaBH₄ /PEG-400 reducing system, followed by an intramolecular cyclization. It was possible to obtain a series of compounds with up to 93 % yield in short reaction times. Among the synthesized products, 2-organyltelluropheno[2,3-b]pyridines have not been described in the literature so far. Moreover, the compounds 2-phenylthieno[2,3-b]pyridine (3 b) and 2-phenyltelluropheno[2,3-b]pyridine (3 c) exhibited significant antioxidant potential in different in vitro assays. Further studies demonstrated that compound 3 b exerted an antinociceptive effect in acute inflammatory and non-inflammatory pain models, thus indicating the involvement of the central and peripheral nervous systems on its pharmacological action. More specifically, our results suggest that the intrinsic antioxidant property of compound 3 b might contribute to attenuating the nociception and inflammatory process on local injury induced by complete Freund's adjuvant (CFA).

Improved Syntheses of the mGlu5 Antagonists MMPEP and MTEP Using Sonogashira Cross-Coupling

The Sonogashira cross-coupling, a key step in the syntheses of the mGlu₅ antagonists MMPEP and MTEP, provided an improved three-step method for the preparation of MMPEP in 62% overall yield. Using Spartan molecular modeling kit an explanation for the failure to employ analogues method in the synthesis of MTEP was sought. The DFT calculations indicated that meaningful isolated yields were obtained when the HOMO energy of the aryl halide was lower than the HOMO energy of the respective alkyne.

Access to functionalized thienopyridines via a reagent-capsule-assisted coupling, thiolation and cyclization cascade sequence

Thienopyridines and related heterocycles were prepared by a reagent-capsule-assisted palladium-catalyzed cross-coupling, thiolation and cyclization process in moderate to good yields.

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.