Photochemical ring expansions of five- and six-membered ring ketones derived from pentoses

Abstract

U.v. irradiation of the six-membered ring ketone, 1,5-anhydro-3,4-O-isopropylidene-L-erythro-pentulose (1), at –70° in ethanol–diethyl ether (1 : 9) gave two ring-expanded isomeric dioxepans (4) in 72% yield; the furanosidulose (5) also underwent ring expansion to give two isomeric dioxan derivatives (6) when irradiated in methanol at room temperature.