In this work, a three-stage
and easily scalable synthesis of 2,6-dicyano-4-pyrone
(overall yield of 45%) as a new convenient building block has been
developed from diethyl acetonedioxalate. It was shown that the transformation
with hydroxylamine and [3 + 2]-cycloaddition, in contrast to the reactions
with hydrazines, selectively proceed through the attack at the cyano
groups without the pyrone ring-opening to give symmetrical and unsymmetrical
pyrone-bearing heterocyclic triads containing 1,2,4- and 1,3,4-oxadiazoles
as well as tetrazole moieties. The reaction of 2,6-bis(hetaryl)-4-pyrones
with ammonia afforded 2,6-bis(hetaryl)pyridines in 63–87% yields.
The 4-pyridone/4-pyridinol tautomerism of 2,6-bis(hetaryl)pyridinols
and the influence of the nature of adjacent azolyl moieties on this
equilibrium have been discussed.
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