Practical Synthesis of an Open Geodesic Polyarene with a Fullerene-type 6:6-Double Bond at the Center: Diindeno[1,2,3,4-defg;1‘,2‘,3‘,4‘-mnop]chrysene

Diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene (1), the smallest possible alkene-centered C60 substructure with a curved pi-system, is obtained in 25-35% yield by flash vacuum pyrolysis of the twisted 1,1'-dibromobifluorenylidene (2) on a 100 mg scale at 1050 degrees C. At 1200 degrees C, the bowl-shaped hydrocarbon 1 rearranges to the planar isomer diindeno[5,6,7,1-defg;5',6',7',1'-lmnop]chrysene (14) by a double 5/6 ring-expansion/ring-contraction. X-ray crystallography establishes that the central carbon atoms of 1 are nearly 80% as pyramidalized as the carbon atoms of C60 (POAV angles = 9.0 degrees and 11.6 degrees for 1 and C60, respectively). A four-step synthesis has been developed to prepare the pyrolysis precursor (2) as a mixture of (E)- and (Z)-isomers in 39% overall yield from commercially available 9-fluorenone-1-carboxylic acid (10).