Chiral calix[4]arene-based diphosphites as ligands in the asymmetric hydrogenation of prochiral olefins

Chiral calixarene-based diphosphite ligands 3a–d have been obtained via lower-rim functionalisation of the p-tert-butylcalix[4]arene core. High enantiomeric excesses (up to 94 %) and good activities were obtained in the rhodium-catalyzed asymmetric hydrogenation of prochiral olefins withTADDOL-containing diphosphites 3c,d. This is the first example of chiral calix[4]arene-modified ligands that induce high enantioselectivity in metal-catalysed asymmetric reactions.