Metal-free chemo- and regioselective acylation of pyridine derivatives with alcohols in water
A straightforward acylaltion of pyridine derivatives has been developed using K2S2O8as the oxidant and water as a green solvent. The corresponding 2-acylpyridines were synthesized with high chemo- and regioselectivity in good to high yields. This efficient and practical method could serve as a new tool for the convenient synthesis of 2-benzoylpyridines of interest for future pharmaceutical and chemical applications.
SELECTIVE SUBSTITUTION OF UNPROTONATED PYRIDINES BY ALKYL RADICALS
The reactions of dioxanyl and cyclohexyl radicals with 2- and 3-X-pyridines (X=CN, COMe, CO2Me) give a single substitution product deriving by addition at the 5- and 6-position respectively; with 4-X-pyridines substitution occurs preferentially at the 3-position.If the reactions are carried out with protonated pyridines other positional isomers are obtained.From the synthetic point of view the two procedures are therefore complementary.The change in positional selectivity on passing from unprotonated to protonated aromatic substrates is discussed and interpreted on the basis of the different nature of the transition state of the addition step.
Chianelli, D.,Testaferri, L.,Tiecco, M.,Tingoli, M.
p. 657 - 663
(2007/10/02)
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