Dendritic phosphoramidite ligands

Scheme 8.9 Asymmetric hydrogenation of arylenamides with dendritic phosphoramidite ligands.

Recently, Reek et al. published the synthesis of a 9H,9 H- [4,4 ]bicarbazole-3,3r-diol (BICOL)-based chiral monodentate phosphoramidite ligand, which was functionalized with two different third-generation carbosilane dendritic wedges (Fig. 26) [57]. As reference reaction in the catalytic study, the rhodium-catalyzed asymmetric hydrogenation of Z-methyl-a-acetamido-cinnamate was chosen. Using a ligand-to-rhodium ratio of 2.2 led to enantio-selectivities which were comparable to the results obtained using the parent BINOL-derived monodentate phosphoramidite MonoPhos. 

Figure 4.22 Modular chiral dendritic chiral monodentate phosphoramidite ligands for the Rh-catalyzed asymmetric hydrogenation of a-dehydroamino acid esters.

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