Four cis-(n+ 5)-bromodioxabicyclo[n.2.1]alkanes (12)(n= 2–5) have been prepared from C₅–C₈ cycloalkenes by the sequence singlet oxygenation, bromination, and treatment with silver trifluoroacetate.

Photo-oxygenation of cycloalkenes provides a convenient route to the corresponding cycloalk-2-enyl hydroperoxides (6). Bromination of each of these proceeds smoothly in carbon tetrachloride to afford a mixture of cis-2,trans-3-dibromocycloalkyl hydroperoxide (10) and trans-2,cis-3-dibromocycloalkyl hydroperoxide (11). Except for 2,3-dibromocyclo-octyl hydroperoxide, the major isomer obtained is (10) and the fraction of (10) in the mixture can be increased by silylating (6) with bistrimethylsilylacetamide before bromination and afterwards desilylating the dibromo-adducts by methanolysis. Both (10) and, less efficiently, (11) react with silver trifluoroacetate to give compounds (12), which are readily separated by low-temperature column chromatography from the bromo-trifluoroacetoxy-cycloalkyl hydroperoxides concurrently formed.

Configurational assignments for (10), (11), and (12) have been made on the basis of spectroscopic data and chemical reactions.