5-Bromo-2-chloro-4-fluoro-3-iodopyridine as a Halogen-rich Intermediate for the Synthesis of Pentasubstituted Pyridines.

The 60 individual halopyridine isomers that contain one bromine, chlorine, fluorine, iodine, and H are valuable potential building blocks in medicinal chemistry research, but surprisingly, there has been only one report on the synthesis of just two of them. Herein, we describe simple syntheses of the unique 5-bromo-2-chloro-4-fluoro-3-iodopyridine ( 10 ) and 3-bromo-6-chloro-4-fluoro-2-iodopyridine ( 32 ) using halogen dance reactions. C6 magnesiation of 10 and its 3-phenyl analogue 22 followed by trapping with electrophiles generated a variety of pentasubstituted pyridines with desired functionalities for further chemical manipulations.