Unusual behaviour of bis[ω-hydroxyalkyl]-1,8,4,5-naphthalenetetracarboxylic bisimides in bisimide–lactam ring contraction: experimental and theoretical study

A series of novel [ω-hydroxyalkyl]-1,8,4,5-naphthalenetetracarboxylic bisimides has been synthesised and tested in the bisimide–lactam ring contaction reaction. It was found that N,N′-bis[ω-hydroxyalkyl]-1,8,4,5-naphthalenetetracarboxylic bisimides with short methylene spacer show unusually low reactivity in bisimide–lactam ring contraction reaction common for six-membered bisimides. The molecular modelling results shows that the reason for such a behaviour is deprotonation of one of the hydroxy groups of bisimides destabilising tetrahedral intermediate — the key intermediate in the ring contraction reaction.