New Insights on the Mechanism of Thermal Cleavage of Unsaturated Bicyclic Diaziridines: A DFT Study

A DFT calculations are carried out at UB3LYP/6‐311++G (3df, 2p) levels of theory to study electrocyclic thermal cleavage of four ( R ) derivatives of unsaturated bicyclic diaziridines, 1 X‐ R , to produce corresponding ( Z ) and ( E ) azomethine imides ( 2 X‐ Z , 2 X‐ E , 3 X‐ Z and 3 X‐ E ), where X=H, Me, t ‐Bu and Ph. Cleavage of 1 X‐ R series to form the most stable 3 X‐ Z product, (path 2) is found the favored procedure because of delocalized negative charge on five atoms and lower steric effect in related transition state. According to IRC calculations in paths 1 and 2, C 6 N 1 bond is cleaved before the rate determinating step (transition state). The stability of unsaturated bicyclic diaziridines and their corresponding ( Z ) and ( E ) azomethine imides is in the following order in gas phase and chloroform, tetrahydrofuran, and acetone solvents: 3 X‐ Z < 3 X‐ E < 2 X‐ Z < 2 X‐ E < 1 X‐ R < 1 X‐ S .