Benzene bicyclic structure

Oxepins and their bicyclic valence tautomers, arene oxides are discussed in <95CHE(42)197>. Particularly noteworthy is the synthesis of a stable benzene oxide (63) which surprisingly shows little tendency to isomerize to the corresponding oxepin (64) in spite of the expectation that the fluorines would greatly destabilize the three-membered ring in the bicyclic structure (63) (Scheme 10) <90JA6715>. 

In this paper we present evidence, based primarily on NMR data that, for a copolymer prepared in toluene or benzene, a mixture of the symmetrical and unsymmetrical bicyclic structures is obtained. Our studies rest largely on heretofore unavailable model compounds which are representative of the substructural units. 

Beckmann rearrangement, 406 Benzene, resonance structure. 192 structure, 189 Benzenonium ion, 205 Benzhydrol, 269 Benzidine rearrangement, 422 Benzyne, 217 Bicyclic compounds, 162 Birch reduction, 200 Bischler-Napieralski reaction, 460 Boat and chair forms, 168 Boiling point, influences on, 212 Bond dissociation, 37 Bond order, 17 Bond stretching, 233 Bonding orbitals. 14 Bredt s rule, 168 Bromonium ion. 100 Brbnsted. 42... 

The Grob fragmentation is a useful synthetic tool for the construction of rings with six to eight members beginning with a bicyclic structural moiety. One example enables the production of substituted benzenes from readily available bicycles. Khan demonstrated that polyhalogenated (chloro and bromo) phenols (e.g., 36) result from treatment of bicyclic ketones (e.g., 35) with PTSA in toluene. ... 

The reaction of the enamines of cyclohexanones with a,ft-unsaluraled sulfones gives mixtures resulting from attack of the enamine at the a- and /(-carbons of the oc,/ -unsaturated sulfone. The ratio of x- and /1-adducts is dependent upon the reaction solvent, the geometry and structure of the sulfone1 4. The diastereoselectivity of these reactions is also poor. The reaction of lithium enolates of cyclic ketones with ( )-[2-(methylsulfonyl)ethenyl]benzene, however, gives bicyclic alcohols, as single diastereomers, that result from initial -attack on the oc,/ -unsaturated sulfone5. 

Recently, molecular orbital calculations (MP2/6-31G //RHF/6-31G level) which cover a series of bicyclic systems from the stable bicyclic compound 109 to the unknown 6,8-dioxabicyclo[5.1.0]octa-2,4-diene (2,3-epoxyoxepin, 120), as well as the two intermediate 8-oxa- (121) and 6-oxa- derivatives (122), were carried out58. These structures are interesting because the bicycle 120 is suggested as a transient intermediate in the metabolic oxidation of benzene leading to the muconaldehyde, which is responsible for the hema-totoxicity of benzene. 

Pure computational results indicate that it should be possible to observe bond fixation in angularly distorted benzenes. Structural studies, either experimental or high-level computational, show that simple cyclic annelations are ineffective at inducing such bond fixation. Computational investigations of arenes with bicyclic annelations predict that these systems will show the desired bond fixation, trisbi-cyclo[2.1.1]hexabenzene, is the favored structure. 

Following this work on NMR spectra of ozonides, there is an extensive paper by the Griesbaum group" where 35 ozonides (6-14 with different stereochemistries) have been studied. The widely different structures examined allowed the influences of structural features on "O NMR spectra of ozonides to be shown. Five structurally different types of ozonides can be recognized symmetrically tetrasubstituted (type 6), unsymmetrically tetrasubstituted (type 7), unsymmetrically tri- and tetrasubstituted (type 8), unsymmetrically disubstituted (type 9-13) and bicyclic ozonides (type 14). "O NMR chemical shifts of peroxidic and ethereal oxygens are collected in Table 3. All spectra were obtained at natural isotopic abundance, in benzene-dg solution mainly at 25 °C, although in some cases higher temperatures had to be used. These experimental conditions make for an easy comparison with the previously discussed data. 

The diastereoselectivity is reversed in the alkylation of the enolate derived from the structurally very similar bicyclic lactam, tetrahydro-3-phenyl-l//.577-pyrrolof 1,2-c]oxazol-5-one (3). Thus, the major diastereomer 4 produced has the tram relationship between the newly introduced substituent in the pyrrolidine ring and the fused oxazolidine ring residue11,12. Only active electrophiles such as iodomethane, 3-halopropenes or (halomethyl)benzenes react11,12. Base-catalyzed equilibration of the product obtained by reaction with 3-bromocyclohexene gives a 50 50 mixture of the cis- and rra s-diastereomers11. 

From the cyclooctatriene - bicyclooctadiene equilibrium, it is possible to trap the structure containing the four-membered ring with dienophiles, e.g. maleic anhydride, including those cases where the bicyclic isomer is only present in small amounts. For example, the dimer of cyclooctatetraene 7 on reaction with maleic anhydride gives the 1 1 adduct 8 in refluxing benzene and the. n 7-tricyclo[4.2.0.02,5]oclane derivative 9 in refluxing toluene.62... 

By treating norbornene with benzenesulfonyl azide in benzene at room temperature, a crystalline product is obtained in quantitative yield.264-265 On the basis of chemical and nmr evidence, an aziridine structure (85) similar to exo-2,3-epoxy-norbornene (86) is attributed to the adduct. The addition thus occurs at the least hindered exo side of the bicyclic nucleus. 

The monocyclic terpene hydrocarbons, many of which are formed readily from the acyclic terpenes by ring closure or from the bicyclic terpenes by ring fission, contain a six-carbon ring and may all be considered as derivatives of either cyclohexane or benzene. They may also be classified, on the basis of common larger fundamental structures, into two distinct types of substituted six-carbon ring structures ... 

Bryce-Smith [2] in 1959. They found that benzene and maleic anhydride react to form a stable 1 2 adduct under the influence of ultraviolet radiation. The authors proposed that initially an ortho adduct is formed which could normally be expected to revert rapidly to the starting materials, but which would be stabilized by rapid addition of a further molecule of maleic anhydride to the bicyclic diene system. The stereochemistry of the 1 2 adduct was established by Grovenstein et al. [23] (who reported that they had independently discovered the same reaction) and, more firmly, by Bryce-Smith et al. [24] and Pettit et al. [25], The structure is depicted in Scheme 4. 

Numerous structures containing the thiocarbonyl ylide dipole are conceivable. Incorporation of the thiocarbonyl ylide dipole into a bicyclic heterocyclic system is possible by the conversion of the cyclic thione (203) into the ring-fused mesoionic system (204). The thiocarbonyl ylide dipole (205) undergoes cycloaddition with both alkenic and alkynic electron-poor dipolarophiles in refluxing benzene or xylene so that, after extrusion of hydrogen sulfide or sulfur, respectively, from the initial 1 1 cycloadducts (206) and (207), a ring-fused pyridinone is formed. The method has been used for the annelation of pyridinones to the imidazole, 1,2,4-triazole, thiazole and 1,3,4-thiadiazole systems... 

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