The stereoselective and short-step synthesis of N-protected allo-carnosadine, ent-carnosadine, and carnosadine lactam was accomplished from a common cyclopropane intermediate. The inter-intramolecular double alkylation of diethyl malonate with an optically active 2-methylaziridine derivative gave the key cyclopropane in excellent yield and optical purity. The following monohydrolysis of the diester moiety using different reaction conditions provided both diastereomers of monoacids, which were converted to three carnosadine derivatives in 5-6 steps from the common diester.