Chapter 6.1 Six-membered ring systems: Pyridines and benzo derivatives

Abstract

This chapter provides information on six-membered ring systems, including pyridines and benzo derivatives. Pyridines and their benzo-derivatives have played an important role in the synthesis of biologically active synthetic and natural substances. Transition metal catalysis, radical reactions, and cycloaddition chemistry-based methods have been developed for the construction of this important ring system. The chapter presents a discussion on the methods developed for the synthesis of pyridines, quinolines, isoquinolines, and piperidines. One main emphasis in the area of pyridine synthesis has been the application of cycloaddition strategies. The use of the pyridyl nitrogen as a directing influence on chemical reactions is discussed. While pyridine N -oxides are normally synthesized via the pyridine, the direct construction of these systems was reported by cyclization of vinamidinium salts in a [3+2+1] annulation reaction. The utilization of organometallic reagents in the construction of quinolines and quinoline intermediates continues to be an area of great interest. Catalytic Rh(I) complexes were used to catalyze the cyclization of N -aryl trifluoracetimidoyl chlorides with internal and terminal alkynes. One routine method for the functionalization of quinolines is the addition of substituents to the 2-position.