N-heterocyclic moieties are abundant among pharmaceuticals and agrochemicals, but a challenge for metalorganic and organocatalytic transformations. We present tripeptides of the type H-Pro-Pro-Xaa as catalysts for stereoselective conjugate addition reactions between N-heterocyclic substituted aldehydes and electrophiles. Alkyl substituents at the N-terminal proline, the reactive site, were crucial for high chemo-and stereoselectivity. Different N-heterocyclic moieties, even at both reaction partners, were readily tolerated and products were obtained in yields of 61-95% and enantioselectivities of up to 98% ee.