A versatile new catalyst for the enantioselective isomerization of allylicalcohols to aldehydes: Scope and mechanistic studies

A new planar-chiral bidentate phosphaferrocene ligand (2) has been synthesi zed and structurally characterized. The derived rhodium complex, [Rh(cod)(2 )]BF4, serves as an effective catalyst for asymmetric isomerizations of all ylic alcohols to aldehydes, furnishing improved yields, scope, and enantios electivities relative to previously reported methods. The catalyst is air-s table and can be recovered at the end of the reaction. Mechanistic studies establish that the isomerization proceeds via an intramolecular 1,3-hydroge n migration and that the catalyst differentiates between the enantiotopic C 1 hydrogens.