Reactivity at the interface of chiral amphiphilic dendrimers. High asymmetric reduction by NaBH(4) of various prochiral ketones.
New amphiphilic dendrimers derived from PAMAM and D-gluconolactone were found to induce chirality in the reduction of prochiral ketones by NaBH(4), in heterogeneous (THF) and homogeneous (water) conditions. The third generation of these amphiphilic dendrimers, G(3)G, was found to be a good chiral ligand for the reduction of various prochiral ketones in heterogeneous conditions. Even with substrates well-known to give poor results (especially linear ketones), good enantioselectivities were obtained. It is also important to notice that under heterogeneous conditions (THF) the dendrimer could be recovered by filtration, regenerated, and recycled (up to 10 times), leading to reproducible results in asymmetric reduction of ketones. We have also discussed the reduction of acetophenone in water. Evidence is presented that the selectivity is dominated by the architecture of the dendrimer and some supramolecular ordering in the position of the ketone at the chiral solvating interface. The results obtained showed a correlation between stereoselectivity of the reduction and the compact character of the dendritic particles.
Schmitzer
A R
AR
Laboratoire des Interactions Moléculaires et Réactivité Chimique et Photochimique, UMR no. 5623 CNRS, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France.
Franceschi
S
S
Perez
E
E
Rico-Lattes
I
I
Lattes
A
A
Thion
L
L
Erard
M
M
Vidal
C
C