A unique, platinum-catalyzed, direct C-H acylation of 2-(aryloxy)pyridines with acyl chlorides is discovered. The reaction requires neither an oxidant nor other additives. When both ortho positions of the aryl group are accessible, the double acylation occurs readily to produce the diacylated products. Aliphatic, aromatic, and α,β-unsaturated acyl groups can all be introduced. The acylation reaction may proceed through an analogous aromatic electrophilic substitution triggered by the nucleophilic attack of the platinum at the acyl chloride.
Platinum-catalyzed
selective C–H acylation of 2-aryloxypyridines
with ethyl chlorooxoacetate provides an efficient way of introducing
an α-keto ester functional group. The reaction is oxidant-free,
additive-free, and, more significantly, free of any decarbonylative
side reactions. The reaction tolerates a variety of substituents from
strongly electron-donating to strongly electron-withdrawing groups.
Double acylation is feasible for 2-phenoxypyridine and its derivatives
with only one substituent at the para position. Although the reaction
of 2-(2-methylphenoxy)pyridine with ethyl malonyl chloride did not
produce the desired β-keto ester, the reaction with ethyl succinyl
chloride proceeded smoothly to give the γ-keto ester. Ethyl
chlorooxoacetate is much more reactive than ethyl succinyl chloride
in this Pt-catalyzed C–H acylation reaction.
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