An Evaluation of Some Hindered Diamines as Chiral Modifiers of Metal-Promoted Reactions

Abstract

Diamino analogues of the C₂-symmetric chiral diphosphine ligands DuPHOS and BPE have been prepared and evaluated as chiral modifiers of the osmium tetraoxide dihydroxylation of stilbene. NMR experiments showed that these ligands were too bulky to coordinate to osmium. Less hindered analogues of these ligands were prepared and some were shown to act as ligands in dihydroxylation reactions but with poor enantioselectivity (e.e. < 10%). The diamines have also been briefly evaluated as ligands in rhodium-catalyzed hydroformylation and copper-catalyzed phenolic coupling reactions. Once again, only low enantioselectivity was obtained.