Asymmetric Trienamine Catalysis for the Construction of Structurally Rigid Cyclic α,α-Disubstituted Amino Acid Derivatives

2,4‐Dienals are shown to undergo highly stereoselective Diels–Alder reactions with olefinic azlactones by asymmetric trienamine catalysis. The obtained cycloadducts are easily transformed into the corresponding cyclic α,α‐disubstituted N‐protected amino acid methyl esters under mild reaction conditions. Furthermore, it is demonstrated that in situ ligation of the crude cycloaddition products with amino acid hydrochloride salts leads to the formation of non‐natural dipeptide motifs in a one‐pot fashion.