2+2]-Photocycloaddition Reactions of Tetronic Acid Esters and Amides

Abstract

Tetronic acid esters and amides, which are readily available from the corresponding tetronic acids, serve as useful starting materials in an intra- or intermolecular [2+2]-photocycloaddition reaction. Typical reaction conditions are irradiation at λ = 254 nm in diethyl ether or an alcohol as the solvent. The bi-, tri- or tetracyclic products so obtained can be further utilized by ring opening either of the lactone or the cyclobutane ring. Lactone ring opening led to the use of a tetramide photocycloaddition product as a conformationally restricted β-proline analogue and to an application of a tetronate photocycloaddition product in the total synthesis of punctaporonin C.