Synthetic Approaches of Six Membered N-Heterocycles Using Bridged N-Based Ionic Liquids: A Review

Six-membered nitrogen-containing heterocycles represent a significant class of compounds in organic chemistry and play a pivotal role in various fields. Conventional synthetic methods of these compounds have certain advantages, but they are also limited by many factors including environmental impacts. Nitrogen-containing bridge-head basic compounds like hexamethylenetetramine (HMTA), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,4-diazabicyclo[2.2.2]octane (DABCO), and 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) have shown promising characteristics in developing task-specific ionic liquids. These ionic liquids have been employed in synthesizing six-membered nitrogen-containing heterocyclic compounds in accordance with the principles of green and sustainable chemistry. Hence, this manuscript has been compiled on recent developments in the synthesis of six-membered nitrogen-containing heterocycles using bridge-head nitrogen-based ionic liquids. The manuscript covers studies published from 2013 onwards.