Synthesis of azocines by ring expansion

The eight-membered N-heterocyclic compounds are among the natural products that show important biological activities. Over the past many years, various methods have been developed for the formation of medium ring systems. Different cyclization reactions are available for the synthesis of five- and six-membered ring systems, but methods for the preparation of seven-, eight-, and nine-membered ring heterocyclic compounds are not as abundant. The medium rings are challenging to synthesize due to entropic and enthalpic factors. Therefore, medium ring heterocyclic compounds are synthesized from acyclic substrates by fewer available approaches based on general cycloaddition or cyclization reactions.