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The cyclic vinylcyclopropane 6a reacts at elevated temperatures with iron pentacarbonyl to selectively give the enone 7a in 52% yield. Reducing the reaction time provided the isomeric ketones 7a–b. Partial chromatographic separation of this mixture allowed the complete spectroscopic identification of 7b by 1H NMR. The structure of 7c was determined from selected spectral data of the mixture of 7a and 7c. For comparison, the methyl substituted derivate 6b was subjected to a carbonylation under the above conditions exclusively providing 8 ini 42% yield. A mechanistic rationale for the two different modes of ring opening is presented.