Stable spiro-endoperoxides by sunlight-mediated photooxygenation of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-alpha-D-xylo-oct-1,4-furano-7-uloses

Sunlight-mediated photooxygenation of 3-O-acetyl and 3-O-methyl derivatives of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-α-d-xylo-oct-1,4-furano-7-uloses (1a-e) in carbon tetrachloride solution gave stable 4,7-epidioxy derivatives in 4R (2a-e) and 4S (3a-e) configurations. The presence of an endo alkyl, on the 1,2-O-alkylidene group and its size, resulted in an increase of the yield of the 4S isomers. 3-O-Acetyl derivatives yielded products as a mixture of C-7 anomers, whereas 3-O-methyl derivatives gave pure single stereoisomers.