The improved synthesis of ROCKYPhos and its application for the asymmetric hydrogenation of dihydroisoquinoline derivatives

An optimized approach to the multigram synthesis of [(1R,2R,3S)-(+)-1,2-dimethyl-2,3-bis(diphenylphosphinomethyl)cyclopentyl]methanol (ROCKYPhos, CatASium I®), a camphor-derived chiral diphosphine ligand, has been developed. The key improvement in the synthetic scheme involved the oxidative cleavage of 3,9-dibromocamphor with V2O5 – HNO3 or NH4VO3 – Cu(NO3)2 – HNO3 system, which gave the corresponding dicarboxylic acid in the yield of 28% and significantly reduced the reaction sequence. The NMR study of a diselenide derivative of ROCKYPhos showed that one of the PPh2 groups had strong donor properties comparable to those of trialkylphosphines. The asymmetric hydrogenation of N-acetyl-1,2-dihydroisoquinoline-4-carboxylates in the presence of ROCKYPhos provided target tetrahydroisoquinolines with up to 52% ee – an outstanding result for this substrate class.