Diastereoselectivity Felkin-Anh Transition State

Additions to Carbonyl groups can be diastereoselective

Background Colour:

Click the structures and reaction arrows in sequence to view the 3D models and animations respectively

The Felkin-Anh conformation has the largest (and most electronegative in other cases) group perpendicular to the carbonyl. Attack on the Bürgi-Dunitz trajectory leads to the nucleophile, hydride in this case, passing close the substituents on the alpha carbon. The nucleophile, in this case hydride, attacks from the least hindered approach.

Link to chelation-controlled example