Cyclizations of enyne-allenes to form persistent biradicals and polycyclic aromatic hydrocarbons with carbon frameworks represented on the surface of C?? [electronic resource] /
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.
School:West Virginia University
School Location:USA - West Virginia
Source Type:Master's Thesis
Keywords:allene biradicals polycyclic aromatic hydrocarbons
Date of Publication: