AbstractRing‐opening reactions of 3‐arylaziridine‐2‐carboxylic esters with various nucleophiles are described. Racemic methyl 3‐(4‐methoxyphenyl)‐, 3‐phenyl‐ and 3‐(4‐nitrophenyl)aziridine‐2‐carboxylate (1a, 1band1c, respectively) were selected as substrates. In the absence of acid, no ring opening occurred. On treatment with ethereal hydrogen chloride,1agave a mixture of diastereomers2a, whereas1band1cgave mixtures of regioisomers2b/3band2c/3c, respectively. Boron‐trifluoride etherate catalyzed reaction of1awith benzenethiol and indole also resulted in the formation of diastereomeric ring‐opened products4aand6a, respectively, due to the electron‐releasing properties of the p‐methoxy group. Only C3 attack was observed. Under the same conditions,1band1cgave a cleanSN2‐type ring opening, leading to diastereomerically pure products4b, 4c, 6band6c. Reaction of1bwith acetic acid gave 7 in anSN2‐type ring opening at C3, followed by an O→N acyl shift. Treatment of enantiopure (+ )‐(2S,3R)‐1bwith benzenethiol, indole and acetic acid gave the corresponding enantiomerically pure β‐functionalized α‐amino acid derivatives. Functionalization of1bat nitrogen strongly increased the reactivity:N‐acylaziridine8isomerized totrans‐oxazoline11when tr