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.

Flash vacuum pyrolysis of 2,3-dihydro-l,4-diazepines in the range 450-550 "C involves interaction of the saturated portion of the molecule with the vinamidine system and causes 1,5-hydrogen shifts which have been established by deuterium labelling experiments; at higher temperatures, ring contraction occurs to give pyrazines as major products.

Gas-Phase Pyrolysis of 2,3-Dihydro-1,4-diazepines: Involvement of the Saturated Portion of the Ring in Chemical Reactions and Novel cis-trans Isomerization of a Fused Ring System. -The observed cis-trans isomerization of fused diazepine systems (I), ( III) is explained mechanistically by sequential 1,5-hydrogen shift (no yields given). -(ELLIS, M. J.; LLOYD, D.; MCNAB, H.; WALKER, M. J.; J. Chem. Soc., Chem.