New monoterpene-derived phosphinopyridine ligands and their application in the enantioselective iridium-catalyzed hydrogenation

Pyridine derivatives with a phosphine or phosphinite pendant (1–11) have been synthesized from (+)-α-pinene, (−)-isopinocampheol, and/or (+)-camphor via Kröhnke annulation or another annulation method as the key step for the construction of the pyridine nucleus. The iridium complex of 6 proved to catalyze hydrogenation of the prochiral unfunctionalized alkene 44 with 94% ee, whereas the complex of 2 was most efficient in the hydrogenation of the cinnamyl-type ester 45 (83% ee).