This award is the starter grant increment of Dr. Carreira's Postdoctoral Fellowship in Chemistry. The design and synthesis of structurally well-defined rare earth complexes for the asymmetric catalysis of the hetero-Diels-Alder cycloaddition reaction will be carried out. Systems to be studied include the reactions of achiral aldehydes with funcionalized dienes. Protecting groups on the dienophile will provide a second contact point with the complex to enhance the selectivity of the formation of one diastereomeric transition state. These steric effects will lead to increased product selectivity. %%% The Diels Alder reaction is very versatile in the different kinds of molecules that can be prepared by it. This proposal will study means by which the reaction can be made more selective. The results will lead to the synthesis of new molecules some of which could have important physiological properties.