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.
4-Methylene-4H-pyrans are popular merocyanine dyes, but their functionalization is limited by the Knoevenagel condensation with aromatic aldehydes. In this work, we developed a novel approach for the construction of the...
A straightforward approach for the construction of the new class of conjugated pyrans based on enamination of 2-methyl-4-pyrones with DMF-DMA was developed. 2-(2-(Dimethylamino)vinyl)-4-pyrones are highly reactive substrates that undergo 1,6-conjugate addition/elimination or 1,3-dipolar cycloaddition/elimination followed by substitution of the dimethylamino group without ring opening. This strategy includes selective transformations leading to conjugated and isoxazolyl-substituted 4-pyrone structures. The photophysical properties of the prepared 4-pyrones were determined in view of further design of novel merocyanine fluorophores. A solvatochromism was found for enamino-substituted 4-pyrones accompanied by a strong increase in fluorescence intensity in alcohols. The prepared conjugated structures demonstrated valuable photophysical properties, such as a large Stokes shift (up to 204 nm) and a good quantum yield (up to 28%).
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