Oxepin 10 Indice

The molecules taking part in a valence tautomerization need not be equivalent. Thus, NMR spectra indicate that a true valence tautomerization exists at room temperature between the cycloheptatriene 110 and the norcaradiene (111). In this case one isomer (111) has the cw-l,2-divinylcyclopropane structure, while the other does not. In an analogous interconversion, benzene oxide and oxepin exist in a tautomeric equilibrium at room temperature. 

The spontaneous oxepin-benzene oxide isomerization proceeds in accordance with the Woodward-Hoffmann rules of orbital symmetry control and may thus be classified as an allowed thermal disrotatory electrocyclic reaction. A considerable amount of structural information about both oxepin and benzene oxide has been obtained from theoretical calculations using ab initio SCF and semiempirical (MINDO/3) MO calculations (80JA1255). Thus the oxepin ring was predicted to be either a flattened boat structure (MINDO/3) or a planar ring (SCF), indicative of a very low barrier to interconversion between boat conformations. Both methods of calculation indicated that the benzene oxide tautomer... 

The effect of temperature upon the oxepin-benzene oxide equilibrium has been investigated by NMR and UV methods (67AG(E)385). At lower temperatures the benzene oxide tautomer is preferred. At higher temperatures it is not possible to estimate the proportion of oxepin tautomer by NMR due to the rapid exchange rate. UV spectroscopy however indicates that the proportion of oxepin increases with increasing temperature. 

The metabolism of polycyclic aromatic hydrocarbons by enzymes present in animal livers involves epoxidation as the initial step. As indicated in Section 5.17.1.2, evidence is available to suggest that oxepins (29)-(34) are present as minor contributors to the arene oxide-oxepin equilibrium and thus may legitimately be considered as metabolic intermediates. 

Naphthalene 1,2-oxide (136), a non-K-region epoxide, shows low thermal stability. Anthracene 1,2-oxide, on the other hand, is stable at ambient temperatures for several weeks. Preparation of (+ )-(lR,2S)-anthracene 1,2-oxide (137), using the above method, constitutes the first example of preparation of an optically pure arene oxide. However, the non-K-region oxides of phenanthrene, namely, its 1,2- and 3,4-oxides (47 and 48), obtained from chiral precursors, racemize fast.66 Perturbational molecular orbital calculations indicate that epoxide-oxepin valence tautomerism is possible. However, the oxepin could not be detected by NMR. 

Dimethoxycarbonylbenzene oxide (98) exists in equilibrium with the oxepin form (159), the latter predominating at equilibrium at ambient temperature.8 The NMR spectrum shows temperature dependence, indicating that a considerable amount of the oxide tautomer exists at equilibrium. 4,5-Dimethylbenzene oxide (160) also exists in equilibrium with its corresponding oxepin tautomer (161). ... 

The behaviour of the corresponding hexafluoro derivative of (40b) in solution is somewhat different solutions of hexafluorobenzene oxide in nonpolar solvents are stable at room temperature. In acetonitrile or acetone, the hexafluorobenzene oxide rearranges spontaneously to hexafluorocyclohexa-2,4-dienone and not to hexafluorooxepin. However, NMR measurements in chlorobenzene at various low temperatures indicate the existence of a dynamic equilibrium between perfluorobenzene oxide and perfluoro-oxepin [289]. 

The control of furan versus oxepin manifolds has been addressed recently. Vinyloxiranes of type (139) yielded oxepins (140) at lower temperatures, whereas higher temperatures gave dihydrofurans (141 Scheme 29), indicating that the Cope-type rearrangement of cis-divinyloxirane may be controll by precisely defining the temperature profile of the flash vacuum pyrolysis. 

Structural information in the crystalline state can be obtained directly by x-ray diffraction studies, but this method has not been used extensively in the arene oxide-oxepin series since the majority of the monocyclic arene oxide-oxepins synthesized to date have been liquids and since chemical instability at ambient temperature is a common feature of many mono- and polycyclic arene oxides. X-ray crystal structure analysis has been carried out on the relatively stable K-region arene oxides 2-4. ° Similarly, an x-ray analysis of 5, a crystalline annelated benzene oxide (which, however, exists in both arene oxide and oxepin form in solution), has been reported and indicates that the six-membered ring is almost planar. The oxepin ring in compound 6 has been shown to exist in the boat conformation both in solution and in the crystalline state. The structural information thus obtained in the crystalline state is totally consistent with the spectroscopic data and the chemical reactivity of the arene oxides in solution and has been used in theoretical studies of the arene oxide-oxepin system. ... 

Enantiomeric analysis of a new antiinflammatory agent in rat plasma using a chiral p-cyclodextrin stationary phase" (71). The R,R S,S enantiomers of the investigational antiinflammatory agent trans-6,6a,7,10, 10a,ll-hexahydro-8,9-dimethyl-U-oxodibenz[b,e]-oxepin-3-acetic add (HOA) were resolved on the p-CD CSP after extraction from rat plasma. The mobUe phase was a mixture of 0.05 M potassium dihydrogenphosphate (pH 5.3) and methanol (35 65, v/v) the flow rate was 1.0 mL/min and the temperature was 22 1 C. The results of the study indicated that the inactive (—) enantiomer was cleared from the plasma more rapidly than the active (+) isomer. 

Systematic and trivial names are both commonly in use for heterocyclic compounds. The systematic names consist of one or more prefixes from Table 1.2 with multipUers where needed designating the heteroatoms, followed by a suffix from Table 1.3 to give the ring size with an indication of the unsaturation. This is preceded by substituents. Thus, oxepin is a... 

The atmospheric chemistry of benzene oxide/ox-epin, a possible intermediate in the atmospheric oxidation of aromatic hydrocarbons, has been investigated by visible and UV photolysis. The results indicated that the major atmospheric sinks of benzene oxide/oxepin are the reaction with OH radicals and photolysis and under smog chamber conditions, with high NO2 concentrations, also reaction with NO3. 

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