Asymmetric Henry Reaction Using Cobalt Complexes with Bisoxazoline Ligands Bearing Two Fluorous Tags.

The effect of the presence of fluorous tags in bisoxazoline ligands on the stereoselectivity of the cobalt-catalyzed asymmetric Henry reaction was investigated. In contrast to the stereoselectivity obtained with conventional nonfluorous ligands, using bisoxazoline bidentate ligands featuring two fluorous tags in adjacent positions on the aromatic ring yielded a reversed stereoselectivity. The stereoselectivity also reversed when the fluorous tags were replaced with alkyl chains of equivalent length, albeit to a considerably lesser degree, highlighting the effect of the fluorous tags.