The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Pyrans

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.

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References in periodicals archive

Series Compound 4,6,4' [formula not reproducible] 4,6 [formula not reproducible] 6,4' [formula not reproducible] 4,4' [formula not reproducible] Thio [formula not reproducible] Furoquinolinones (FQ) [formula not reproducible] Dihydro [formula not reproducible] Other angelicins [formula not reproducible] Chromone [formula not reproducible] 3,4 [formula not reproducible] Difuro [formula not reproducible] Triazole [formula not reproducible] Allo [formula not reproducible] Pyran [formula not reproducible] Coumarin [formula not reproducible] TABLE 2: [IC.sub.50] values calculated after 48 h from treatment of IB3-1 cells with serial dilutions of TMA derivatives.

Differential Effects of Angelicin Analogues on NF-[kappa]B Activity and IL-8 Gene Expression in Cystic Fibrosis IB3-1 Cells

Safarzaei, "Potassium sodium tartrate as a versatile and efficient catalyst for the one-pot synthesis of pyran annulated heterocyclic compounds in aqueous media," Research on Chemical Intermediates.

Kinetic and mechanistic investigation of pyrano[2,3-d]pyrimidine formation in the presence of catalyst under novel one-pot three-component reaction

This agreement confirms the validity of the TPSSH/[6-311++G.sup.**] level of theory in the prediction of the electronic absorption of squaraine dyes and pyran compounds.

Pyran-squaraine as photosensitizers for dye-sensitized solar cells: DFT/TDDFT study of the electronic structures and absorption properties

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.

Avanti Systems

Aloke Dutta, 'We have developed an innovative triple reuptake inhibitor, D-578, based on a unique pyran molecular scaffold to address the current therapeutic needs for PTSD and other neurological disorders.

Tonix Pharmaceuticals Expands Preclinical Pipeline with Triple Reuptake Inhibitor, TNX-1600, for the Treatment of PTSD

This latter case, regardless of position of the proton abstracted, is confirmed by the augmentation of O-H PDE value of phenyl ring attached to heterocyclic pyran ring of daidzein compared to that of its homolog in 6-hydroxydaidzein [36] in the gas phase.

The Substitution Effect on Reaction Enthalpies of Antioxidant Mechanisms of Juglone and Its Derivatives in Gas and Solution Phase: DFT Study

In [sup.1]H-NMR spectrum of this compound, two flaw peaks are seen at [delta] = 4.26 and [delta] = 4.07 which are related to the methoxy and CH (C-3) of Pyran ring groups.

Synthesis of pyranopyrimidine derivatives using a practical one-pot three-component reaction in the presence of L-proline catalyst

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).

Characterization of phytoconstituents in leaf extracts of forest species for textile applications

The presence of a pair oxygenated methines at ([[delta].sub.H] 3.95, [sup.1]H, d, J = 4.8, H-3"; [[delta].sub.C] 69.7, C-3") and ([[delta].sub.H] 6.55, [sup.1]H, d, J = 4.8, H-4"; [[delta].sub.C] 63.5, C-4") indicated that an oxygen atom at C-7 was cyclized with C-2" to form a dioxo-substituted pyran ring.

Cytotoxic activities of flavonoids from Centaurea scoparia

They have a large structural variability and more than 600 isoflavones have been identified to date and are classified according to oxidation level of the central pyran ring (Figure 1).

Flavocoxid, a nutraceutical approach to blunt inflammatory conditions

Alum (KAl[(S[O.sub.4]).sub.2].12[H.sub.2]O) was found to be effective in the synthesis of cis-isoquinolic acids [16a], mono- and disubstituted 2,3-dihydroquinazolin-4(1H)-ones [16b], dihydropyrimidines via Biginelli reaction [16c], coumarins [16d], 1,3,4- oxadiazoles [16e], dibenzoxanthenes [16f], 1,5-benzodiazepines [16g], trisubstituted imidazoles [16h], mono and bis(spiro-2-amino-4H pyran)[16i] etc.

Alum promoted synthesis of 2H-indazolo[2,1-b]phthalazinetrione derivatives in water