A strategy for the stereoselective synthesis of unsymmetric atropisomeric ligands: preparation of NAPhePHOS, a new biaryl diphosphine.
MeO-NAPhePHOS represents the first example of a new series of atropisomeric diphosphines bearing heterotopic biaryl moieties. The key step of its synthesis is the diastereoselective, intramolecular, Cu(I)-promoted coupling of 1-iodonaphthol and 2-iodo-3-methoxyphenol connected by a chiral tether. (R,R)-2,4-Pentanediol is used as the chiral auxiliary in this highly selective reaction that leads to a single enantiomer of the title diphosphine. In the Ru-promoted hydrogenations of carbonyl derivatives, NAPhePHOS affords enantioselectivity levels fully comparable to those of the C(2)-symmetrical analogues, BINAP and MeO-BIPHEP respectively, thus showing that the lack of C(2) symmetry is not detrimental to the catalytic properties of atropisomeric ligands in these hydrogenation reactions.
Michaud
Guillaume
G
Laboratoire de Synthèse Sélective Organique et Produits Naturels ENSCP-11, rue Pierre et Marie Curie, 75231 Paris Cedex 05 France.marinet@ext.jussieu.fr
Bulliard
Michel
M
Ricard
Louis
L
Genêt
Jean-Pierre
JP
Marinetti
Angela
A