Base-Promoted Rearrangement of 1,5-Dibromopentacyclo2,5.03,9.04,8>decane-6,10-dione: Easy Entry of a Novel Cage System, 10-Oxa-9-oxopentacyclo2,4.03,6.05,8>decane

Article abstract of DOI:10.1246/bcsj.66.2068

The Diels-Alder dimerization of 2-bromo-2,4-cyclopentadienone ethylene acetal (2) gave endo-2,7-dibromodicyclopentadiene-1,8-dione 1,8-bis(ethylene acetal) (3) as a minor product in a 4.5percent yield. Ultraviolet irradiation of 5 led to dimerization product 7. Deacetalization was accomplished by treating with concentrated sulfuric acid to give 1,5-dibromopentacyclo<5.3.0.0^2,5.0^3,9.0^4,8>decane-6,10-dione (9). Compound 9 was converted into a new cage system, 10-oxa-9-oxopentacyclo<5.3.0.0^2,4.0^3,6.0^5,8>decane, in a high yield by treating with 5percent aqueous potassium hydroxide at 80 deg C.