Synthesis of optically active dendrimers having chiral bisphosphine as a core

First and second generation chiral dendrimers P-1G1, P-2G1, P-1G2 and P-2G2 containing chiral bisphosphine as a core were synthesized via a reaction of chiral bisphosphine compound (S,S)-1 with benzyl ether dendrons. This is the first example of chiral dendrimers containing chiral phosphorus atoms. To investigate the effect of chiral phosphorus atoms on their conformations, optically inactive dendrimer P'-2G1 was synthesized as well using optically inactive initiator 1' which was the mixture of rac-1 ((S,S)-1 and (R,R)-1) and meso-1. Their structures were characterized by H-1, C-13, P-31 NMR, and HRMS. According to CD measurement, optically active dendrimers exhibited the Cotton effect induced by the chirality of phosphorus atoms, while optically inactive dendrimer P'-2G1 showed no Cotton effect.