Photochemical synthesis of a 4,5-dihydrofuroazetidinone, a novel β-lactam system

2,4-Dimethyl-3-phenylisoxazole anhydrobases were easily prepared from the corresponding 5-chloroisoxazolium trifluoromethanesulfonate and carbon anions of 1,3-dioxo compounds in the presence of triethylamine. Photorearrangement of 2-(2,4-dimethyl-3-phenyl-2H-isoxazol-5-ylidene)malonic acid diethyl ester gave a 4,5-dihydrofuroazetidinone in good yield.