Pyridines 39Palladium(0)-catalysed reactions
Extensive use has been made of palladium(0)-catalysed cross-couplings using halopyridines, pyridine triflates,
pyridine Grignard reagents and zinc derivatives, pyridine stannanes, pyridine boranes and boronic acids. A small
selection of illustrative examples is shown below. Note that pyridin-2-ylboronic acids are quite unstable (in the
presence of base), but the N-phenyldiethanolamine ester gives the right balance between stability and reactivity
for successful cross-couplings. Pyridin-3-ylboronic acids are much more stable and react normally without spe-
cial precautions.
Oxidation and reduction
In contrast to the aromatic ring of benzenoid compounds, the pyridine ring is easily reduced, for example with hydro-
gen over a platinum catalyst in acidic solution. It is certainly the N-protonated pyridine that is reduced and thus
N-alkyl pyridinium salts are also easily reduced, with hydrogen and a catalyst.