Synthesis of chalconoid-like compounds and their [2 + 2] photodimerizations in solution and theoretical calculations

Chalconoid-like compounds; (2E,4E)-1,5-diphenylpenta-2,4-diene-1-one (1), (2E,4E)-1-(p-ethyl)phenyl-5-phenylpenta-2,4-diene-1-one (2), (2E,4E)-1-(m-methyl)phenyl-5-phenylpenta-2,4-diene-1-one (3) and (2E,4E)-1-(p-methyl)phenyl-5-phenylpenta-2,4-diene-1-one (4) have been synthesized and their (2 + 2) photosensitized cycloaddition reaction gave four new δ-truxinic-type dimers in solution: rel-(1β,2α)-dibenzoyl-rel-(3β,4α)-di-(E)-(2-phenyl)ethenylcyclobutane (5), rel-(1β,2α)-di-(p-ethyl)-benzoyl-rel-(3β,4α)-di-(E)-(2-phenyl)ethenylcyclobutane (6), rel-(1β,2α)-di-(m-methyl)-benzoyl-rel-(3β,4α)-di-(E)-(2-phenyl)ethenylcyclobutane (7) and rel-(1β,2α)-di-(p-methyl)-benzoyl-rel-(3β,4α)-di-(E)-(2-phenyl)ethenylcyclobutane (8), stereoselectively. The possible dimerization products of compound 1 were calculated theoretically. Experimental and theoretical calculations showed that δ-truxinic-type dimer is the most stable isomer of all.