Cyclizations of enyne-allenes to form persistent biradicals and polycyclic aromatic hydrocarbons with carbon frameworks represented on the surface of C?? [electronic resource] /

by Zhang, Hai-Ren.

Cyclization of Enyne-Allenes to Form Persistent Biradicals and Polycyclic Aromatic Hydrocarbons with Carbon Frameworks Represented on the Surface of C60 By Hai-Ren Zhang Thermolysis of 1,1’-(1,2-ethynediyl)bis[9-bis(4-tert-butyl)phenyl]ethenylidene-9Hfluorene (benzoenyne-allene) in 1,4-cyclohexadiene (1,4-CHD) at 75 °C produced the cycloaromatized adduct 8,16-bis[bis(4-tert-butyl)phenyl]methyldiindeno[1,2,3-hi:1’,2’,3’qr]chrysene in 22% yield. The reaction presumably proceeds through a cascade sequence involving an initial Myers cyclization reaction to form a biradical having an ?,3didehydrotoluene moiety in its structure. The subsequent trapping of the aryl radical center in this initially formed biradical with the tetraarylallenic moiety intramolecularly affords a biradical having two stabilized triarylmethyl radical centers. A subsequent hydrogen-atom abstraction from 1,4-CHD, manifesting its radical character, then produces 8,16-bis[bis(4tert-butyl)phenyl]methyldiindeno[1,2,3-hi:1’,2’,3’-qr]chrysene. Similarly, thermolysis of 9- diarylethenylidene-1-phenylethynyl-9H-fluorenes in 1,4-CHD furnished 1-diarylmethyl-2phenylfluoranthenes in essentially quantitative yields. The presence of the fused fivemembered ring in the above benzoenyne-allenes is necessary to direct the initial biradicalforming step toward the Myers cyclization reaction. Without the five-membered ring as in the cases of 1,1,3-triaryl-3-[2-(arylethynyl)-1-phenyl]-1,2-propadiene, the C2-C6 cyclization reaction became the preferred pathway, leading to 5,10,11-triaryl-11H-benzo[b]fluorenes. The C44H26 hydrocarbon, a benzo[ghi]fluoranthene derivative, was synthesized in 13% overall yield in eight steps from acenaphthenequinone and 2 equiv of 1-(2ethynylphenyl)-2-phenylethyne. Condensation of 5’,5’-dimethylspiro[acenaphthylene-1 (2H),2’-[1,3]dioxan]-2-one (the monoketal of acenaphthenequinone) with the lithium 2-(2phenylethynyl)phenylacetylide afforded the corresponding benzoenediynyl propargylic alcohol. On exposure to thionyl chloride, the benzoenediynyl propargylic alcohol underwent a cascade of reactions with the formation of the chloro-substituted benzoenyne-allene in situ followed by a C2-C6 cyclization to produce a benzofulvene biradical, leading to the formal Diels-Alder adduct and subsequently, after tautomerization, a chloride of an indane fused cyclopenta[def]phenathrene. Reduction with sodium borohydride then gave the corresponding ketal. Deprotection of the ketal group produced the corresponding ketone to allow a repeat of condensation with 2-(2-phenylethynyl)phenylacetylide followed by the cascade transformation to afford the chlorinated derivative of the C44H26 hydrocarbon. Subsequent reduction then furnished the C44H26 hydrocarbon having a carbon framework represented on the surface of C60.