Oxidation hexamethyl Dewar benzene

In 1-aryl-1,2-epoxy cyclohexenes, a significant salt effect has been observed in favor of the formation of m-diol products. A diol is obtained from hexamethyl Dewar-benzene oxide via an intermediate with carbonium ion character (Eq. 301). ... 

In contrast to previous reports, treatment of hexamethyl Dewar benzene oxide (312) with aqueous acid yielded the diol (314) via a kinetically con-... 

Fig. 23. ESR spectrum obtained upon oxidation of hexamethyl-(Dewar)-benzene with SbCl5 at —78 °C (top) and simulation [374]...

Fig. 25. Time resolved CIDNP spectrum observed upon photo-induced electron transfer oxidation of hexamethyl-(Dewar)-benzene (0.02 M) by chloranil (0.02 M). The top spectrum was observed 5 ps after excitation with the frequency-tripled output (355 nm) of a Nd/YAG laser. The bottom spectrum was recorded in the dark...

The fate cS the contact ion pair [RH A 1 is critical to electrm-transfer oxidation. Oxidative efficimey is the highest with those organic donors diat yield unstable radical cations, such as hexamethyl(Dewar benzene), which und goes spontaneous rearrangement (equation 7). > ... 

Osmium tetraoxide has also been used in the oxidation of bicyclic and polycyclic dienes. Thus, oxidation of norbomadiene (26) in a stoichiometric reaction was found to yield the exo-cis diol exclusively. On the other hand, in the NMO catalytic system a mixture of the exo-cis and endo-cis products was reported. However, by use of the NMO catalytic procedure for the substituted norbomadiene 27, the exc-diol was formed exclusively at the sterically crowded unsubstituted double bond and this product was utilized in the synthesis of pentalenolactone. Somewhat surprisingly, oxidation of hexamethyl Dewar benzene (28) exclusively gave the endo-cis diol as sole product. The tricyclic compound 29 gave the usual c/s-diol oxidation product of one of the double bonds. ... 

Polymethyl 3a,4,7,7a-tetrahydroindoxazenes (77) are obtained by thermal rearrangement of the benzonitrile oxide-hexamethyl-Dewar-benzene cycloadducts (76).90 Reaction of 2,4,6-trimethylbenzonitrile oxide with 3,6-dimethyl-p-benzoquinone yields the 4,7-dioxo-3a,4,7,7a-tetrahydroin-doxazene78(Ar = 2,4,6-Me3C6H2) or its regioisomer, and addition proceeds similarly with 2,6-dimethyl-p-benzoquinone. In a number of other examples, nitrile oxides were found to cycloadd to the C=0 bond of quinones.91... 

The thermally stable bis-ozonide (1,2,4-trioxolane) of hexamethyl Dewar benzene has been isolated and its X-ray structure determined [94T7625]. Bicyclic oxadithiolane (93) has now been prepared by intramolecular reaction between dithiirane and ketone functions [94AG(E)777]. An efficient synthesis of benzotrithiole oxide (94) has been reported [93SUL5] and the stable benzotriselenole (95) has been prepared [94CC1593]. 

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