The photochemical dimerization of 3 known methoxy derivatives of chalcones, (2E)-1-(2-methoxy)phenyl-3-phenylpropen- 1-one (1), (2E)-1-(3-methoxy)phenyl-3-phenyl-propen-1-one (2), and (2E)-1-(4-methoxy) phenyl-3-phenylpropen-1-one (3), yielded 3 new delta-truxinic type dimers in solution: rel-(1beta,2alpha)-di-(2-methoxy)-benzoyl-rel-(3beta,4alpha)-diphenylcyclobutane (4), rel-(10,2a)-di-(3-methoxy)benzoyl-rel-(3beta,4alpha)-diphenylcyclobutane (5), and rel-(1beta,2alpha)-di-(4-methoxy)benzoyl-rel-(3beta,4alpha)-diphenylcyclobutane (6), stereoselectively. Precursor chalcones showed high superoxide radical scavenging activity although the dimers were inactive.