SYNTHETIC STRATEGIES TOWARDS C-60 - MOLECULAR MECHANICS AND MNDO STUDY ON SUMANENE AND RELATED STRUCTURES

Strain energies of the hydrocarbons derived from the fragments of C60 along the C5, C3 and C2 symmetry pathways indicate that the strain ene rgy per carbon (E(s)) increases gradually along the C3 and C2 paths, b ut has a maximum at C40H10 along the C5 path. C21-Sumanene, 10, has be en recognised as a leading fragment along C3 route with an inversion b arrier of 24.2 kcal mol-1 and a bowl depth of 1.15 angstrom at MNDO le vel. This contrasts with C20-corannulene, 6, which is a more shallow b owl with a lower inversion barrier. The bond alternation in the centra l six membered ring of sumanene resembles that of C60. The higher frag ments en route to C60 are deep bowls with higher barriers for inversio n. An approach to sumanene via a triphenylene derivative, 26, has been probed and an increase in strain through sequential placement of meth ylene bridges has been estimated, using MNDO and MM2 calculations. Syn thetic routes to a doubly bridged triphenylene, 28, and schemes for fu rther elaboration of 26a and sumanene derivative, 29, towards C60 are considered.