Asymmetric hydrogenation is one of the most important enantioselective reactions. Although the hydrogenation, transfer hydrogenation, and hydrosilylation of various substrates in the presence of metal catalysts have been described, the asymmetric reduction of aromatic and heteroaromatic compounds still represents a great challenge. This situation is particularly true for the enantioselective hy...

Radically different! The hydrosilylation of pyridines and quinolines is strictly 1,4-selective and likely involves an ionic one-step rather than the established radical two-step hydride transfer from a ruthenium(II) hydride complex onto the respective pyridinium and quinolinium ion intermediates (see scheme; Ar(F) =3,5-(CF3)2C6H3). Even 4-substituted substrates react highly regioselectively. Is...

The reaction of 3-oxo-3-phenyl-2-phenylhydrazonal with functionally substituted and heteroaromatic substituted acetonitrile to yield arylazonicotinic acid derivatives and 5-arylsubstituted pyridines was established. In some cases the produced nicotinates could not be isolated as they underwent thermally induced 6π-electrocyclization yielding polynuclear pyridine derivatives.

Chlorination with equimolar POCl₃ can be efficiently achieved not only for hydroxypyrimidines, but also for many other substrates such as 2-hydroxy-pyridines, -quinoxalines, or even -amides. The procedure is solvent-free and involves heating in a sealed reactor at high temperatures using one equivalent of pyridine as base. It is suitable for large scale (multigram) batch preparations.

A Chan-Lam reaction has been used to prepare N-alkenyl-α,β-unsaturated nitrones, which undergo a subsequent thermal rearrangement to the corresponding tri- and tetrasubstituted pyridines. The optimization and scope of these transformations is discussed. Initial mechanistic experiments suggest a reaction pathway involving oxygen transfer followed by cyclization.

A convenient, one-pot, two-component synthesis of 2-(1-amidoalkyl)pyridines is reported, based upon the substitution of suitably-activated pyridine N-oxides by azlactone nucleophiles, followed by decarboxylative azlactone ring-opening. The synthesis obviates the need for precious metal catalysts to achieve a formal enolate arylation reaction, and constitutes a formally 'umpoled' approach to thi...

A Rh(iii)-catalyzed cyclization of azoles with alkynes has been developed. A variety of azole-fused-pyridines were obtained in good to excellent yields and regioselectivity. Both the C5 and the C4 position of azoles were suitable for the reaction.

An operationally efficient CDI mediated tandem coupling and cyclization reaction to generate [1,2,4]triazolo[4,3-a]pyridines has been reported. The reaction conditions and scope were investigated, and the methodology was demonstrated in batch mode as well as in a continuous process.