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The synthesis of the title compound 7 has been achieved by irradiation of the fourfold bridged tricyclo[4.2.0.0 [2, 5] ]octa-3,7-diene 6 ; the latter species was prepared by the AlCl 3 supported dimerization of cyclododeca-1,7-diyne. © 1997 Elsevier Science Ltd.

In the crystal of octamethylcuneane (1,2,3,4,5,6,7,8-octamethylpentacyclo[3.3.0.0 2,4 .0 3,7 .0 6,8 ]octane), C 16 H 24 , there are two independent molecules in the asymmetric unit. Octamethylcubane(1,2,3,4,5,6,7,8-octamethylpentacyclo[4.2.0.0 2,5 .0 3,8 .0 4,7 ]octane), C 16 H 24 , exhibits crystallographic 3m symmetry. Due to the eclipsed orientation of the methyl groups in octamethylcubane, the average bond length is extended to 1.563 (3) A compared with cubane itself. In the cuneane derivative, the cage bond lengths vary between 1.517(2) and 1.573(2)A in accordance with their bicyclic character and the repulsive forces between the methyl groups. The exocyclic bonds to the methyl C atoms in both molecules are shortened due to the increased s character of the cage C atoms.

The reaction of cyclic diynes with either CpCo(CO)2 or AlCl3 yielded strained hydrocarbons in which a Dewar benzene or a tricyclo[4.2.0.02,5]octa-3,7-diene frame is bridged by hydrocarbon chains. The photochemistry and thermochemistry of these species are discussed. Results of quantum chemical calculations (DFT, CASPT2) are used to discuss the thermochemistry of four different fourfold bridged tricyclo[4.2.0.02,5]octa-3,7-dienes. Depending on the bridging mode, either a Cope-type rearrangement or a ring opening reaction is preferred. Copyright © 2002 John Wiley & Sons, Ltd.