En route to archimedene: total synthesis of C3h-symmetric [7]phenylene.

ABSTRACT

[reaction see text] The total synthesis of C(3)(h)-symmetric [7]phenylene has been accomplished by triple cobalt-catalyzed cycloisomerization of an appropriate nonayne. Its spectral data are in accord with the expectations for a triply angularly fused system, but its calculated heat of formation suggests the presence of a destabilizing sigma effect relative to its D(3)(h) isomer. The molecule constitutes the largest substructure of archimedene hitherto synthesized.