Photo-oxidative cleavage of a furan-azetidinone carbon-carbon bond: a synthesis of 4-acetoxyazetidinone

A stereoselective synthesis of the 4-acetoxyazetidinione (1) from methyl 3(R)-hydroxybutyrate is reported. The synthesis involved stereoselective preparation of a 4-(2-furanyl)azetidinone that was allowed to react with singlet oxygen. The resulting endoperoxide intermediates underwent direct rearrangement to an acyloxyazetidinone that on reaction with sodium acetate gave 1 in modest yield. An improved yield of 1 was obtained by treatment of the endoperoxides with hydrogen peroxide followed by acetic anhydride to give an α-alkoxy acylperoxide that underwent thermal rearrangement to 1