Carbonyl group of ketone is more deshielded than carbonyl group of ester due to deshielding effect of
pyrone ring [42].
Naringenin is a naturally occurring polyphenolic compound containing two benzene rings linked together with a heterocyclic
pyrone ring [16].
pyrone type, chromene, diketone, or quinone groups) and delocalised [pi]-electrons of the basal planes are assumed to have a basic nature (Contescu et al.
It is a member of a group of naturally occurring compounds, the flavonoids, which have a common flavone nucleus composed of two benzene rings, linked through a heterocyclic
pyrone ring.
Recent studies have involved nitrogen and oxygen heterocycles, particularly compounds of the pyridine and
pyrone families, and the techniques of chromatography (including HPLC), mass spectrometry, GCMS, chemical ionization mass spectrometry and NMR (both 1H and 13C) are used extensively.
Epoxydons and a
pyrone from the marine-derived fungus Nigrospora sp.
The ethylenic double bond of 4-oxo-4H-benzopyran-3-carbaldehyde (3-formyl chromone) is a very reactive system towards nucleophiles, owing to the presence of aldehydic and
pyrone carbonyl groups linked to it [23].
[sup.13]C-NMR spectrum of 4a showed characteristic absorptions responsible for 11 carbon atoms at [delta]164.5 ppm for C = O, [delta]151.6 and [delta]114,1 ppm for
pyrone C, [delta]147.2 ppm and [delta]145.5 ppm for triazole C and 5144.9, [delta]128.1, [delta]125.3, [delta]125.0, [delta]124.9, [delta]119,6 ppm for aromatic C.
ether, quinone,
pyrone), which are less reactive than the hydrophilic groups (e.g.