N,N-Dimethylformamide dimethyl acetal transforms an allylic OH group,
which is part of a tetracyclic hydrocarbon in a unique elimination rea
ction into a [5.5.5.5]fenestradiene (2b --> 4). In topologically selec
tive reactions of this diene 3 with [Fe-2(CO)(9)], the [Fe(CO)(4)(eta(
2)-diene)] and the (Fe(CO)(3)(eta(4)-diene)] complexes 8 and 9, respec
tively, are formed by complexation on one side of the diene moiety, wh
ereas complexation on the other side leads to a [Fe(CO)(2)(Cp)] comple
x 10.