Aromaticity oxygen heterocycles

An attractive example is the pigment of red roses, which is an interesting aromatic oxygen heterocycle (an anthocyanidin). Two of the phenolic OH groups are present as (5-glycosides. 

Polycyclic aromatic compound Polycyclic aromatic hydrocarbon Polycyclic aromatic sulfur heterocycle Polycyclic aromatic oxygen heterocycle Nitrogen-containing polycyclic aromatic compound (both heterocyclic and nonheterocyclic compounds) Secondary-nitrogen polycyclic aromatic nitrogen heterocycles (nitrogen in a five-membered ring)... 

Ruonne atoms in aromatic nitrogen heterocycles are readily replaced by oxygen nucleophiles [77] Bistnfluoromethyl hydroxylarmne anion is an mterest-ing nucleophile for the mtroduction of oxygen mto perfluoropyndine Rearrangement of the product occurs at 125 °C [18] (equation 12)... 

Colby J, DI Stirling, H Dalton (1977) The soluble methane mono-oxygenase of Methylococcus capsulatus (Bath). Its ability to oxygenate -alkanes, -alkenes, ethers, and alicyclic, aromatic and heterocyclic compounds. Biochem J 165 395-401. 

Girgis, M. J., and Gates, B. C., Catalytic Hydroprocessing of Simulated Heavy Coal Liquids. 2. Reaction Networks of Aromatic Hydrocarbons and Sulfur and Oxygen Heterocyclic Compounds. Ind. Eng. Chem. Res, 1994. 33 pp. 2301-2313. 

Heterocycles Both non-aromatic unsaturated heterocycles and heteroaromatic compounds are able to play the role of ethene dipolarophiles in reactions with nitrile oxides. 1,3-Dipolar cycloadditions of various unsaturated oxygen heterocycles are well documented. Thus, 2-furonitrile oxide and its 5-substituted derivatives give isoxazoline adducts, for example, 90, with 2,3- and 2,5-dihydro-furan, 2,3-dihydropyran, l,3-dioxep-5-ene, its 2-methyl- and 2-phenyl-substituted derivatives, 5,6-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene, and 1,4-epoxy-l,4-dihydronaphthalene. Regio- and endo-exo stereoselectivities have also been determined (259). 

Chiral 10 to 12-membered nitrogen and oxygen heterocycles, fused to isoxazo-line rings have been prepared with high regio- and stereoselectivity by INOCs of tethered N- and O-allyl carbohydrate derivatives. The use of a -Y-Ar-CH2 tether, containing a 1,2-disubstituted aromatic ring between the heteroatom attached to... 

Aromatic and heterocyclic cleavage involves a hydrocarbon being separated from an oxygen atom, which functions to link it to another moiety of the molecule this process may lead to a decrease in the initial toxicity. The metabolic effects of microorganisms differ with the molecular configuration of the product, which affect aromatic or heterocyclic ring cleavage differently. 

In addition to the examples of diene cyclisations described above there are reports of alkoxyallenes as precursors of five- to seven-membered oxygen heterocycles <99TL1747>. Of interest here is the cyclisation of 45 to 46 in 88% yield in the presence of Pd(0 Ac)2-dppb complex. The same reagent system has also been used in the regioselective lactonisation of steroids where the aromatic ring of estrone is fused to a seven-membered lactone <99TL1171>. 

Schmid, E. R., G. Bachlechner, K. Varmuza, and H. Klus, Determination of Polycyclic Aromatic Hydrocarbons, Polycyclic Aromatic Sulfur, and Oxygen Heterocycles in Cigarette Smoke Condensate, Fresenius Z. Anal. Chem., 322, 213-219 (1985). 

The term 4-oxo-flavonoids includes a group of complex polyphenols that share a common structure of diphenylptopanes (C6-C3-C6) characterized by two aromatic rings and an oxygenated heterocycle, Fig. (3). The three rings are referred to as the A, B, and C (or pyrane) rings. 

Colby, J., D. I. Stirling, and H. Dalton, The soluble methane monooxygenase from Methylococcus copsulatus bath - Its ability to oxygenate n-alkanes, ethers and alicyclic, aromatic, and heterocyclic compounds , Biochem. J., 165, 395-402 (1977). 

Other aromatic ketones undergo photocyclization to form oxygen heterocycles. Methyl o-benzyloxyphenylglyoxylate (400) is converted in high yield into a mixture of the isomers (401 and 402).415 The stereochemistry of the cyclization is both solvent- and temperature-dependent, the former isomer (401) being formed almost exclusively in nonpolar solvents such as heptane or benzene, and in each case an excited triplet appears to be involved. The related aldehyde, O-benzylsalicylaldehyde (403), is similarly converted into cis-2-phenyl-3-hydroxy-2,3-dihydrobenzofuran (404), but in much lower yield a second product may possibly be the tram isomer.410... 

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