THERMAL TRANSFORMATION OF RING-OPENED [2-60 DIMER INTO A WIDE-BRIDGEDC-120 ISOMER - A COMPUTATIONAL EVALUATION OF FULVALENE-NAPHTHALENE REARRANGEMENTS(2]C)

As a continuation of the studies on thermal transformation of the [2+2 ] C-60 dimer (1), the consequence of the pyracylene-rearrangement-like valence isomerization of the fulvalene partial structure at the bridg e of the ring-opened product from 1, namely 2, was searched by dynamic reaction coordinate/AM1 semiempirical MO calculations. It is predicte d that the fulvalene bridge of 2 rearranges into naphthalene partial s tructure by the concerted 'in-plane' mechanism to give a wide-bridged C-120 intermediate having twenty five-membered rings and two ten-membe red rings (3). The computed energy of activation (145 kcal/mol) is 40 kcal/mol lower than those computed for pyracylene rearrangements. In c ontrast, the recently reported analogous rearrangement of indigo (13) to dibenzonaphthyridindione (14) is computed to occur by the stepwise 'sp(3)' mechanism.