Benzobarrelenes, formation

Scheme 4. Mechanism of formation of products in the bromination of benzobarrelene.

The hydrogen-labeled benzobarrelene indicates that the formation of benzo-cyclooctatetraene from the direct photolysis takes place predominantly via benzovinyl bridging<44) j... 

Both thermal (120 °C at 0.005r) and photochemical decomposition of the tosylhy-drazone salt (21) were proposed to proceed by initial formation of the cyclopropyl-carbene followed by fragmentation to biradicals (22) and (23), which proceeded to 1- and 2-vinylnaphthalene and benzobarrelene (24). ... 

A similar reaction in which an aryne has been postulated as intermediate is the formation of benzobarrelene (200) from 5-amino-[3,3]paracyclophane (201). 

OSiMej) under the usual condition results in the silyloxycyclopropane (61). However, by performing the cyclopropanation in the presence of acetyl chloride (60 R = OSiMej, R = H) is converted directly into the cyclopropyl ester (62). " The styryl ether (63) does not react under the conditions of the Conia modification but, by employing diethylzinc, cyclopropanation is readily effected. To bring about cyclopropanation of the vinyl ether (60 R = OMe or OEt, R = H) without the formation of significant amounts of 2-alkoxymethylenecyclohexane carefully controlled conditions are necessary. " The use of diethylzinc also has the beneficial effect of increasing the product yiel in the reaction between benzobarrelene and di-iodomethane. Although all of the possible products are produced, the anti-tricyclic system (64) is by far the major product (30%). 

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