The photochemistry of ketones derived from carbohydrates. Part 8. Type I cleavage of 1,2:4,5-di-O-isopropylidene-β-D-erythro-2,3-hexodiulose-2,6-pyranose: a synthesis of D-ribulose from D-fructose

Abstract

Solutions of di-O-isopropylidene-β-D-erythro-2,3-hexodiulose-2,6-pyranose (8) in various solvents decarbonylate upon irradiation with u.v. light to give an anomeric mixture of 1,2:3,4-di-O-isopropylidene-D-ribulose (10) and (11), accompanied by variable amounts of the unstable olefin (12) and the aldehyde (13). Compound (13) was found to be a thermal breakdown product from the olefin (12). The photoproduct yields were sensitive to the solvent polarity. The furanose derivatives (10) and (11) were produced with a 1.2 : 1.0 ratio in 30, 35, and 45% yields in methyl cyanide, benzene, and n-hexane, respectively. The D-ribulose derivatives (10) and (11) were produced on a preparative scale, isolated free from (12) and (13) by distillation, and hydrolysed to D-ribulose.