Halogenation by the appropriate amounts of bromine or N-bromosuccinimide converts spirodiisophora-3',6-dione successively into the 4'-ax-mono- and 2',4'-diax-dibromo-3',6-dione. The latter is reduced by lithium aluminium hydride to the corresponding 6,3'-ketol. with retention of one or both bromo-substituents, depending on conditions. The bromoketones undergo the Favorski ring-contraction under the influence of alkalis to compounds of the bicyclo[2.2.2]octane-2-spirocyclopentane ring-system .

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... e 13C NMR spectra of the individual products are assigned and correlated with their structures.