The enantioselective synthesis of elecanacin through an intramolecular naphthoquinone-vinyl ether photochemical cycloaddition

Elecanacin, an unusual cyclobuta-fused naphthalene-1,4-dione derivative isolated from the bulbs of Eleutherine Americana Merr. et Heyne (Iridaceae) has been obtained, together with its epimer isoelecanacin, by a 2 + 2 cycloaddition resulting from irradiation of 5-methoxy-2-(2-vinyloxypropyl)-naphthalene-1,4-dione. The synthesis of enantiopure elecanacin starting with (R)-propylene oxide has established the absolute configuration of the natural product and has revealed that the sample isolated from the bulbs possessed an enantiomeric excess of only 14%.