Torquoselectivity Induced by Lone-Pair Conjugation in the Electrocyclic Reactions of 1-Azapolyenes

Torquoselectivity in the electrocyclic interconversions of 1-azapolyenes and their heterocyclic isomers was investigated theoretically. The ring openings of 1,2-dihydroazete, 1,2-dihydropyridine, and 1,2-dihydroazocine were examined using HF, MP2, and B3LYP calculations. A large preference for inward rotation of the nitrogen lone pair and outward rotation of the N−H group was found for the four- and six-electron systems. No strong preference was observed for the eight-electron system.