Densely substituted unnatural l- and d-prolines as catalysts for highly enantioselective stereodivergent (3 + 2) cycloadditions and aldol reactions

(3 + 2) Cycloaddition reaction between azomethine ylides and π-deficient alkenes leads to densely substituted L- and D-unnatural prolines. These (3 + 2) cycloadducts in turn catalyse the preparation of an offspring of unnatural endo- and exo-L-proline derivatives. These latter compounds are also efficient catalysts of aldol reactions and yield aldol adducts with the opposite stereochemistry obtained under natural L-Pro organocatalysis.