UNSATURATED 8-MEMBERED RING COMPOUNDS .6. CHEMISTRY OF BENZOCYCLOOCTATETRAENE

Benzocyclooctatetraene (I) can be conveniently synthesized by Diels-Alder addition of butadiene to 1,2-dehydrocyclooctatetraene (V) followed by dehydrogenation of the dihydro compound (VII) produced. By using 1,2-dimethylenecyclobutane as the diene the benzocyclooctetraene (IX) was synthesized. The formation of benzocyclooctatetraeneiron tricarbonyl (X) and a benzocyclooctatetraenediiron hexacarbonyl tentatively formulated as XVII is described. The bromination of I afforded 3,4-dibromo-3,4-dihydrobenzocyclooctetraene (XVIII) which underwent facile rearrangement to 1,2-benzocyclohepta-1,3,5-triene-7-aldehyde (XIX) on chromatography. Nitration gave a mixture of mononitro compounds thought to be the 4-, 5- and 3-nitro compounds XXIII, XXIV, and XXV, respectively. Reaction of I with tetracyanoethylene gave the adduct (XXVII), while reaction with dimethyl acetylenedicarboxylate afforded XXXII, formally by 1,6 addition. The mechanism of this reaction is discussed. © 1969, American Chemical Society. All rights reserved.