Abstract
A series of 1,8‐dichloroanthracene precursor molecules with substituents in C‐10 position of different steric demand (cyclohexyl, tert‐butyl, methyl, isopropyl, n‐butyl, phenyl, benzyl, trimethylsilylethinyl) were synthesised and subjected to electrocyclic cycloadditions with chlorobenzyne generated from 3‐chloroanthranilic acid. The aim was to steer the regioselectivity of the addition reaction by the steric repulsion between this C‐10 substituent and the chlorine substituent at the benzyne intermediate. With H as C‐10 substituent the reaction leads to 23 % syn and 77 % anti form. With the small methyl group a syn/anti ratio of 37:63 was achieved. Contrary to our expectations the large C‐10 substituent tert‐butyl leads to 100 % selectivity for the anti form. The best results were achieved for the C‐10 substituent n‐butyl with a syn/anti ratio of 40:60. The crystal structures of five 1,8‐dichloroanthracenes with C‐10 substituents were determined, namely those with tert‐butyl, cyclohexyl, n‐butyl and phenyl groups. As expected the backbone of the tert‐butyl compound shows marked distortion of the planarity. Additionally, the crystal structures of three triptycenes were determined, namely those of the syn compound 1,8,13‐trichlorotriptycene and those of the anti compounds 10‐tert‐butyl‐1,8,16‐trichlorotriptycene and 1,8,16‐trichloro‐10‐methyltriptycene.