Oxygen heterocycles

Anthocyanins are water-soluble pigments, as acylation of the carbon skeleton by glycosides increases the polarity of these molecules. Furthermore, according to the pH conditions, the heterocyclic oxygen atom may be found in cation form, further increasing the molecule s polarity. 

The reaction of 2-polyfluoroalkylchromones (e.g., 323) with l,3,3-dimethyl-3,4-dihydroisoquinolines (e.g., 324) gave zwitterionic 6,7-dihydrobenzo[ ]quinolizinium compounds such as 326 (Scheme 70). The mechanism proposed for this transformation involves an addition-elimination displacement of the chromane heterocyclic oxygen by the enamine tautomer of the dihydroisoquinoline, followed by intramolecular cyclization of the intermediate 325 <20030L3123>. 

Because of its importance, the application of planar chromatography for the analysis of various secondary metabolites in plants such as heterocyclic oxygen compounds (coumarins, flavonoids, anthocyanins, etc.) has been reviewed many times [143,144],... 

Glucose is first esterified to penta-O-acetylglucose using acetic anhydride. Note that the hemiacetal hydroxyl is also esterified, and thus any equilibration with an aldehyde form is now not possible (see Section 7.2). When this penta-acetate is treated with HBr, the anomeric acetate is preferentially lost under the acidic conditions, due to the stabilization conferred by the heterocyclic oxygen. Note that this is the same type of intermediate we implicated... 

Heterocyclic Nitrogen Compounds Heterocyclic Oxygen Compounds... 

Heterocyclic Oxygen Compounds with Three or More Rings Dibenzofuran... 

HETEROCYCLIC OXYGEN COMPOUNDS WITH THREE OR MORE RINGS... 

Heptachlor under Unsaturated Alkyl Halides Heptanes under Alkanes and Cyclic Alkanes Heterocyclic Nitrogen Compounds Heterocyclic Oxygen Compounds Heterocyclic Sulfur Compounds... 

One- and Two-Ring Oxygen Heterocycles under One- and Two-Ring Heterocyclic Oxygen Compounds Organophosphonates... 

For phorone dioxide (55) H-NMR spectra (66DOK(167)575) show only one conformation, but its structure appears poorly defined dipole moments suggest as more probable the anti orientation of the two heterocyclic oxygen atoms, which appear to be s-cis oriented with respect to the carbonyl group. 

Lactones are cyclic esters derived from lactic acid (CsHeOs). They are constituents of many essential oils and plant volatiles. They contain a heterocyclic oxygen next to a carbonyl function in a five or more membered ring that is saturated or unsaturated. Those with a five-membered ring are called y-lactones, e.g. y-angel-ica lactone 148, whereas compounds containing a six-membered ring are called (5-lactones, e.g. (5-valerolactone 149 (Structure 4.45) [1-4, 6, 9, 22, 23,29, 62]. 

Chelating carboxylates. Furan-2- and thiophene-2-carboxylates are included in Table 70 because the heterocyclic oxygen or sulfur atoms may be bonded to the metal atom. The... 

Spectrometrie de Masse des Heterocycles Oxygenes C. Mercier, Bull. Soc. Chim. Fr., 1969, 4545-4560. 

Much of the synthetic chemistry of xanthones has arisen out of their natural occurrence, a topic which has been reviewed (61CRV591), and also as a result of their incorporation into dyes. There are only two routes of any significance to xanthones and these basically involve ring closure on to either the heterocyclic oxygen atom or the carbonyl carbon atom (Scheme 185). 

Keywords aromaticity, indane, indene, nitrogen-containing heterocycles, oxygen-containing heterocycles, sulfur-containing heterocycles, thermochemistry... 

For benzo[6]furan, detritiation in trifluoroacetic acid at 70°C gave f2 = 17,000, hence hydrogen bonding of the heterocyclic oxygen with the solvent and it is probable that/2 could be 20% higher, with a+ s -0.50. Nevertheless, the 2-position is quite clearly less reactive than the 2-posi-tion of benzo[6]thiophene. 

The structure of ra-complexes has been examined by the X-ray crystallographic studies of solid samples and by the spectral measurement of heterocycle-halogen equilibria in solution. By the former approach the structure of the solid 1 2 pyridine-molecular iodine complex has been shown to consist principally of two pyridine molecules collinearly bonded to an iodine atom and of linear triiodide units. Moreover, in the 1 1 complex of dioxane and bromine, the heterocyclic oxygen-bromine-bromine linkages are also collinear.4 In the latter type of study, interest in the well-known phenomenon of brown iodine solutions has occasioned the measurement of the stability constants for many complexes of halogen and heterocycles.25, 29 Information concerning their structure in solution comes from a consideration of the relative size of such constants as a function of heterocycle structure. Thus, the fact that bromine complexes of both 8-bromo- and 8-methylquinolines possess stability constants (K = 1.1 and 4.8 liters/mole) much smaller than that of quinoline itself... 

---