Deconstructive Pyridylation of Unstrained Cyclic Amines through a One-Pot Umpolung Approach.

A one-pot umpolung method for the ring-opening pyridylation of unstrained cyclic amines was developed using -amidopyridinium salts. This process involves the formation of electron donor-acceptor complexes between bromide and -amidopyridinium salts, ultimately leading to the functionalization of pyridines. This protocol is compatible with a range of 5- or 6-membered cyclic amines and pyridines, thereby providing a powerful synthon for preparing C4-functionalized pyridines under visible-light conditions in the absence of an external photocatalyst.

Visible-Light-Active Coumarin- and Quinolinone-Based Photocatalysts and Their Applications in Chemical Transformations.

Organic dyes have been actively studied as useful photocatalysts because they allow access to versatile structural flexibility and green synthetic applications. The identification of a new class of robust organic chromophores is, therefore, in high demand to increase structural diversity and variability. Although coumarins and quinolinones have long been acknowledged as organic chromophores, their ability to participate in photoinduced transformations is somewhat less familiar.

Enantioselective functionalization at the C4 position of pyridinium salts through NHC catalysis.

A catalytic method for the enantioselective and C4-selective functionalization of pyridine derivatives is yet to be developed. Herein, we report an efficient method for the asymmetric β-pyridylations of enals that involve N-heterocyclic carbene (NHC) catalysis with excellent control over enantioselectivity and pyridyl C4-selectivity. The key strategy for precise stereocontrol involves enhancing interactions between the chiral NHC-bound homoenolate and pyridinium salt in the presence of hexafluorobenzene, which effectively differentiates the two faces of the homoenolate radical.