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heterocyclic compounds that contain an oxygen atom and two conjugated (α-pyrene) or isolated (γ-pyran) double bonds. Pyrans are highly unstable compounds: α-pyran is only known in derivative form, and γ-pyran is a colorless liquid with a boiling point of 84°C (with decomposition; also decomposes rapidly at room temperature).

Dihydropyrans and tetrahydropyrans are most stable and more readily accessible. Important pyran derivatives are αpyrone

and γ-pyrone. The pyran ring is a structural feature of many natural substances. For example, most hexoses (aldoses and ketoses) are essentially six-membered pyranoses.

References in periodicals archive ?
The door is made from Schott's Pyran S fire resistant glass, in either 10mm or 12mm thickness, and is available either on hinges or top and bottom rails and pivots.
Flavonoids represent a large group of polyphenols, characterized by two benzene rings linked via a heterocyclic pyran ring.
The basic structural feature of flavonoids is the 2-phenylbenzopyrane or flavan nucleus, which consists of two benzene rings linked through a heterocyclic pyran ring (Brown 1980).
from the site of infection in vivo by using a pyran polymer-conjugated derivative of Cu, Zn-superoxide dismutase (SOD); this derivative showed a prolonged in vivo [t.
SCHOTTs fire-resistance glass products PYRAN S and PYRANOVA received UK approval for use in the timber doors of six major door blank manufacturers.
Moreover heterocyclic compounds containing pyran ring also present a wide properties of biological activities such as anticancer, spasmolytic, diuretic, anticoagulant [15, 16].
Flavonoids are a polyphenols subclass which are widely distributed in the plant kingdom, and are characterized by two or more aromatics rings, each bearing at least one aromatic hydroxyl and connected with a heterocyclic pyran [4].
Several acclaimed building projects in Europe recently installed fire resistant glazing based on our PYRAN S specialty glass.
Rings A and B are benzene rings and ring C is a heterocyclic pyran or pyrone.