Title dilactam diacid 1 has been synthesised and resolved into enantiomers via diastereomeric salts 2 with a chiral amine; the absolute configuration of (1R,4R)-(–)-1 was established by decarboxylation and transformation into the parent dilactam (1R,4R)-(–)-C; the molecular and crystal structures of (±)-1 and (–)-1 (space groups P2₁/_n and P2₁, respectively) were determined.