Ullmann Coupling Reaction of Bicyclic Amidines DBU/DBN with Aryl Halides: A Pathway to the Synthesis of ϵ‐Caprolactam Derivatives

Abstract

AbstractThis paper demonstrates a selective, mild approach to Ullmann amination of aryl halides to synthesizeN‐alkylated derivatives of ϵ‐caprolactam. The synthetic route involves anin‐situring‐opening of 1,8‐diazabicyclo[5.4.0]undec‐8‐ene (DBU) followed by concurrent arylation with aryl halides in the presence of copper iodide as a catalyst under ligand‐free conditions. This method provides a new entry to a wide variety of ϵ‐caprolactam derivatives in good to excellent yields in a single synthetic sequence. Similarly, other bicyclic amidines such as 1, 5‐diazabicyclo‐[4.3.0]non‐5‐ene (DBN), and 1,5,7 triazabicyclo[4.4.0] dec‐5‐ene (TBD) also showed good to very high reactivity.Azepan‐2‐one, or Caprolactam, is an important synthon in polymer chemistry and has a global demand as it is employed to make Nylon 6 filament, fiber, and plastics.[1]The global caprolactam market size is expected to expand for the growing textile industry with rising demand for plastics in the construction of automotive, electrical, and electronic sectors. Additionally, technological advancements aimed at improving the cost‐effective manufacturing process of caprolactam, to minimize the release of hazardous waste into the environment is of vital necessity. Derivatives of ϵ‐caprolactam are of interest for the production of modified nylons[2]and nanogels.[3]Several Azepinones and their analogs play an important role in medicinal chemistry,[4]used in the synthesis of pharmaceutical drugs including Benazepril,[5]Telcagepant,[6]and Ivabradine.[7]