Dioxa pyrenophane

Other oxidants like thallium(III) oxide, vanadium(V) oxyfluoride, palladium ) acetate, and ruthenium(IV) tetrakis(trifluoracetate) have been developed as powerful tools for the intramolecular biaryl coupling reaction [7,93,113]. Nevertheless, DDQ is still one of the most versatile reagents in oxidative coupling reactions (see Scheme 14 and 29 [82,114]). The highly strained dioxa[8](2,7)pyrenophane (65), portraying an overall curvature of nearly 90° for the pyrene subunit, was finally obtained from the mefa-cyclophanediene (66) by dehydrogenation with DDQ in refluxing benzene in 67% yield [114]. 

Scheme 29. Reaction sequence to the curved dioxa[8](2,7)pyrenophane (65, [114]) a) (MeO)2CHBF4, CH2C12, room temperature, 2h b) fBuOK, THF, 3 h c) fBuOK, THF/ fBuOH = 1/1, room temperature, 3 h d) DDQ,benzene, A, 12 h, 65 (67%),66 (26%)...

Polycyclic aromatic hydrocarbons can be bent by bridging in a similar fashion. Two recent examples of such [n] cydophanes are azulenophane 116 [77] and 1,8-dioxa[8](2,7)pyrenophane 117 [78]. X-ray structure analysis revealed an angle of 3.7° between the azulene ring planes, whereas the pyrene moiety is bent by nearly 90°. 

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