Topospecific Reactions of a [5.5.5.5]Fenestradiene with [Fe 2 (CO) 9 ]

N , N ‐Dimethylformamide dimethyl acetal transforms an allylic OH group, which is part of a tetracyclic hydrocarbon in a unique elimination reaction into a [5.5.5.5]fenestradiene ( 2b → 4 ). In topologically selective reactions of this diene 4 with [Fe 2 (CO) 9 ,], the [Fe(CO) 4 (η 2 ‐diene)] and the [Fe(CO)3(η 4 ‐diene)] complexes 8 and 9 , respectively, are formed by complexation on one side of the diene moiety, whereas complexation on the other side leads to a [Fe(CO) 2 (Cp)] complex 10 .