Corannulenes flash vacuum pyrolysis

The decisive break came in 1991 when Scott and co-workers reported the formation of corannulene from 7,10-diethynylfluoranthene 19 under flash vacuum pyrolysis (FVP) conditions. The critical features of this approach appear to be the high temperature employed (900-1000 °C) and the gas-phase conditions. The high temperature provides energy for drastic fluctuations in 8 away from its equilibrium geometry, allowing the reactive centers to come close enough to form the new bonds while the gas-phase conditions prevent polymerization (although some polymeri-... 

The first synthesis of a semibuckminsterfullerene was accomplished by a procedure analogous to the preparation of corannulene except that 1,2,5,6-tetrake-topyracene served as the starting material (Scheme 5). Flash vacuum pyrolysis of the tetrachloro compound led to a remarkable quadruple ring closure to produce the semi-buckminsterfullerene 27. The NMR shows three methine carbons and five quaternary carbons at 125.5, 126.8, 127.3, 128.6, 136.7, 137.3, 142.0, and 145.4 ppm. The latter signals compare favorably to the single resonance observed at 143 ppm for buckminsterfullerene. 

Cyclopentacorannulene (67) was obtained as a mixture with corannulene (in ratio 7 3) in 10-15% yield from dichloride 66 by flash vacuum pyrolysis at 1,000 °C (Scheme 18) [106]. In contrast, 67 could also be prepared, in 20% yield, by titanium-mediated carbenoid couplings of 68 in solution phase [34]. 

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