CHAIR-BOAT INTERCONVERSION IN CYCLIC SEVEN-MEMBERED AMIDES AND RELATED STRUCTURES.

Article abstract of DOI:10.1016/S0040-4020(01)92036-8

The transition state to ring reversal has been examined in a series of 7-membered rings related to caprolactam.The structural changes associated with introduction of Me groups, with alteration of the nature of the C=N double bond, with ring fusion, or with introduction of a second, nonconjugated N atom perturb the transition state to ring reversal.From 1H and 13C NMR studies, we find that the lactam bond itself favors a different transition state from that present in cycloheptene.With some exceptions, the observed barriers are consistent with TS II, in which ring reversal begins with movement of the C₅ end of the ring, or with TS III, in which ring reversal begins with C₃-C₄ bond torsion.The conclusions are consistent with the structural changes that result from the functional and steric alterations.