The xanthate route to pyridines

Modifying Poly(caprolactone) Degradation through C-H Functionalization

There is a growing need for degradable polymers for applications in sustainable plastics and medical implants. To enhance the utility of degradable polymers, both better understanding of the factors that influence their degradation and new tools to modulate degradation are needed. We report the C-H xanthylation of poly(caprolactone), a biodegradable polyester, which results in changes in materials properties even at small incorporations. Despite the functionalized materials exhibiting a decrease in crystallinity and hydrophobicity, xanthylated poly(caprolactone) degrades more slowly than its unfunctionalized counterpart. To understand this rate difference, kinetic studies with a small-molecule surrogate were performed and demonstrated that functionalization adjacent to the hydrolyzable ester functional group led to slower degradation. This study illustrates how the interplay between molecular and materials characteristics can impact degradation.

Preparation of Substituted Pyridines via a Coupling of β-Enamine Carbonyls with Rongalite-Application for Synthesis of Terpyridines

A Hantzsch-type strategy for the synthesis of 2,3,5,6-tetrasubstituted pyridines via an oxidative coupling of β-enamine carbonyl compounds with rongalite was developed. This method employs rongalite as a C1 unit for the assembly of a pyridine ring at C-4 position, offering a facile method for the preparation of substituted pyridine derivatives with a broad functional group tolerance. In particular, this method allows us to prepare terpyridine derivatives, which are important ligands or structural fragments for catalysts and 3D metal–organic frameworks.

The xanthate route to six-membered carbocycles

Convergent routes to various six-membered carbocyclic architectures exploiting the unique radical chemistry of xanthates are described in this brief review. Three approaches are discussed. The first is the modification of existing cyclohexane building blocks, namely, cyclohexanones, cyclohexenones and cyclohexenes. The second deals with the construction of six-membered carbocycles by associating the chemistry of xanthates with classical ionic reactions, especially the Robinson annulation, the Michael addition and the Horner–Wadsworth–Emmons condensation. Finally, the third route is the formation of six-membered rings by direct six- exo and, but more rarely, six- endo cyclisation modes. Many of the complex structures presented herein would be tedious to obtain by more traditional methods.

Tandem vinyl radical Minisci-type annulation on pyridines: one-pot expeditious access to azaindenones

A new regiospecific alkylative/alkenylative cascade annulation of pyridines has been achieved whilst the corresponding classic Minisci alkylative annulation failed. This protocol provides a novel and expeditious access to azaindenones and related compounds via cross-dehydrogenative coupling with the long-standing problem of C2/C4 regioselectivity of pyridines being well addressed.

Modular Approach to Substituted Pyridoazepinones

Pyridoazepinones are potentially interesting structures, yet they are still underexploited in the medicinal chemistry field and hard to obtain synthetically. We present a general and flexible synthetic route to substituted pyridoazepinones, enabled by the xanthate addition-transfer process, which furnishes the target molecules from readily available starting materials in generally good yields. The method shows good functional group tolerance and allows the preparation of pyridoazepinone scaffolds on gram scale.

Levoglucosenone and Its Pseudoenantiomer iso-Levoglucosenone as Scaffolds for Drug Discovery and Development

The bioderived platform molecule levoglucosenone (LGO, 1) and its readily prepared pseudoenantiomer (iso-LGO, 2) have each been subjected to α-iodination reactions with the product halides then being engaged in palladium-catalyzed Ullmann cross-coupling reactions with various bromonitropyridines. The corresponding α-pyridinylated derivatives such as 11 and 24, respectively, are produced as a result. Biological screening of such products reveals that certain of them display potent and selective antimicrobial and/or cytotoxic properties. In contrast, the azaindoles obtained by reductive cyclization of compounds such as 11 and 12 are essentially inactive in these respects. Preliminary mode-of-action studies are reported.

β-C(sp2)–H alkylation of enamides using xanthate chemistry

Access to the γ-amino-β,γ-unsaturated acyl scaffold was established by applying xanthate chemistry to enamides.