Relative rates of cycloaromatization of dynemicin azabicyclo[7.3.1]enediyne core structures. An unusual change in ΔS‡

Abstract

A series of dynemicin core azabicyclo[7.3.1]enediynes undergo cycloaromatization at dramatically different rates despite the fact that the distance (r, by X-ray diffraction) between the bonding acetylenes is practically identical (3.4 Å); when the carbamate protecting group is removed to give the sec-amine 10, it cycloaromatizes more rapidly, and the entropy of activation changes from a negative to positive.