A pentacene with a 144° twist

9,10,11,20,21,22-Hexaphenyltetrabenzo[a,c,l,n]pentacene (1) was prepared by the reaction of 1,3-diphenylphenanthro[9,10-c]furan with the bisaryne equivalent generated from 1,2,4,5-tetrabromo-3,6-diphenylbenzene in the presence of n-butyllithium, followed by deoxygenation of the double adduct with low-valent titanium. The X-ray structure of 1 shows it to be the most highly twisted polycyclic aromatic hydrocarbon known, with an end-to-end twist of 143.6°. Compound 1 was resolved by chromatography on a chiral support, and the pure enantiomers have specific rotations in excess of 7000°, but the molecule racemizes slowly at 25 °C (t1/2 = 9.3 h, ΔG≠rac = 23.8 kcal/mol). Copyright © 2003 American Chemical Society.