Non‐Electronic Activation of Anthracenes Using Steric Repulsion of the 9‐Substituent with Chloro Groups at the peri‐Positions

We investigated how the introduction of substituent at the 9‐ or 10‐position of the 1,8‐dichloroanthracene framework affects the horizontal and vertical distortions of the anthracene rings. The 9‐substituted anthracenes showed higher distortions than their 10‐substituted counterparts due to the steric repulsion with two chloro groups at the peri ‐positions. The distortion of anthracene framework affected their reactivity. Indeed, 9‐substituted anthracenes exhibited higher reactivity to undergo the Diels–Alder reaction with maleic anhydride, which was a result of non‐electronic activation.