The major product from the photoreaction of 4-methylenedispiro[2,1,2,3]decane (5) with Fe(CO)5 is shown to be a tricarbonyliron σ,π-complex of structure (7), whereas the products from 4-methylenespiro[2,4]heptane (9) and 4-methylenespiro[2,5]octane (15) are the respective bi-cyclic enones (12)–(13) and (16).
Two alternativemodes of addition to vinyl-cyclopropane systems are here described for each of two dienophiles: tetracyanoethylene is shown to react either via[2 + 2] or by [2 + 4] cycloadditions; and dimethyl acetylenedicarboxylate reacts either by the ‘ene’ route or by way of insertion to the double bond.