Computational Studies on the Electrocyclizations of 1-Amino-1,3,5-hexatrienes

Electrocyclizations of 1,3,5-hexatrienes containing up to four electron-donating and/or electron withdrawing substituents have been studied computationally using the hybrid density functional, B3LYP. Electron donating substituents at positions C-1 and C-5 decrease activation barriers by 0.3 to 2.3 kcal/mol. Introducing of an electron-withdrawing group, CO₂Me, at C-4 further decreases the activation energy by 7 kcal/mol. Electron-withdrawing groups (NO₂, SO₂Ph and CN⁺Me₂) at C-2 have a profound effect of 17−25 kcal/mol on the activation energy.