Synthesis and Reactivities of Aromatic Oxides

Synthesis and Reactivities of Aromatic Oxides. The synthesis and absolute configurations of benzene and naphthalene (15,25,3 5,4iS )-diepoxides, (+)-(73) and (+)-(74), have been reported, as have those of the naphthoquinone derivative (2.5,3/ )-(+)-(75).  

Hungerbuehler, D. Seebach, and D. Wasmuth, Helv. Chim. Acta, 1981, 64, 1467. K. Koreeda and M. Yoshihara,/. Chem. Soc., Chem. Commun., 1981, 974. 

Harigaya, H. Yamaguchi, and M. Onda, Chem. Pharm. Bull., 1981, 29, 1321. 

The first examples of syn stereoselective epoxidation of arene dihydro-diols have been reported with the preparation of (82) and (83) from the corresponding diolsThus unexpected -epoxidation has been interpreted as due to the exertion of steric control by the axial benzylic hydroxy-groups, whereas such control is usually exhibited by equatorial hydroxy-groups. 

The optically active benz[a]anthracene oxides (89) and (90) have been synthesized. Thermal recemization (at 293-322 K, in CDCI3) of the chiral chrysene 3,4-oxide (91) has been shown to occur via first-order kinetics, with an activation energy of 25.2 kcal mol The results are consistent with a reaction mechanism involving an oxepine intermediate (92), as predicted by theory. 

Synthesis and Reactivities of Aromatic Oxides. Much of the work in this area is generated from an interest in the carcinogenicity of many of the fused-ring aromatic oxides. Some syntheses of arene oxides and the chemistry of diol epoxides have been reviewed. 

The K-region phenanthrene oxide (68) undergoes photochemical ring-enlargement to (69) via the singlet excited state. A similar photochemical rearrangement for the K-region 3,4-epoxy-3,4-dihydropyrene was also reported. 

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Synthesis and Reactivities of Aromatic Oxides. Certain optically active arene oxides, which are of biological significance as metabolites of polycyclic aromatic hydrocarbons (PAH), undergo spontaneous racemisation. The most plausible mechanism for this involves ring opening to the corresponding oxepins... 

Synthesis and Reactivities of Aromatic Oxides 14 Miscellaneous Methods 16... 

Nitrile oxides are widely used as dipoles in cycloaddition reactions for the synthesis of various heterocyclic rings. In order to promote reactions between nitrile oxides and less reactive carbon nucleophiles, Auricchio and coworkers studied the reactivity of nitrile oxides towards Lewis acids. They observed that, in the presence of gaseous BF3, nitrile oxides gave complexes in which the electrophilicity of the carbon atom was so enhanced that it could react with aromatic systems, stereoselectively yielding aryl oximes 65 and 66 (Scheme 35). ... 

H. Schumann, J. A. Meese-Marktscheffel, and L. Esser, Synthesis, Structure, and Reactivity of Organometallic rc-Complexes of the Rare Earths in the Oxidation State Ln3 + with Aromatic Ligands, Chem. Rev. 95, 865-986 (1995). 

Schumann, H., Meese-Marktscheffel, J.A., and Esser, L. (1995) Synthesis, structure, and reactivity of organometallic Jt-complexes of the rare earths in the oxidation state Ln + with aromatic ligands. Chemical... 

One of the breakthroughs in the field was reported in 1983 by Mimoun and coworkers . On that occasion they reported the synthesis, characterization and radical reactivity of a class of vanadium peroxo complexes representative of which is the species V0(02)pic (HaOIa, 36. The oxidative ability of this complex has been tested with several aliphatic and aromatic hydrocarbons and the synthetic results obtained can be summarized as in Scheme 20. 

Properties. Vanillin is a colorless crystalline solid mp 82-83 °C) with a typical vanilla odor. Because it possesses aldehyde and hydroxyl substituents, it undergoes many reactions. Additional reactions are possible due to the reactivity of the aromatic nucleus. Vanillyl alcohol and 2-methoxy-4-methylphenol are obtained by catalytic hydrogenation vanillic acid derivatives are formed after oxidation and protection of the phenolic hydroxyl group. Since vanillin is a phenol aldehyde, it is stable to autoxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxyl group and by aldol condensation at the aldehyde group. Several of these derivatives are intermediates, for example, in the synthesis of pharmaceuticals. 

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