Synthesis of a C44H26 hydrocarbon having a carbon framework represented on the surface of C60 via benzoenyne-allenes

The C44H26 hydrocarbon 20 was synthesized in 13% overall yield in eight steps from acenaphthenequinone (6) and 2 equiv of 1-(2-ethynylphenyl)-2-phenylethyne, Condensation of the monoketal 7 with the lithium acetylide 8 afforded the benzoenediynyl propargylic alcohol 9. On exposure to thionyl chloride, 9 underwent a cascade of reactions with the formation of the chloro-substituted benzoenyne-allene II in situ followed by a C2-C6 cyclization to produce the biradical 12, leading to the formal Diels-Alder adduct 13 and subsequently, after tautomerization, the chloride 14. Reduction with sodium borohydride then gave 15. Deprotection of the ketal group produced 16 to allow a repeat of condensation with the acetylide 17 followed by the cascade transformation to afford the chloride 19. Subsequent reduction then furnished the C44H26 hydrocarbon 20 having a carbon framework represented on the surface of C-60.