Synthesis and reactivity of η⁴-diene-Fe(CO)₃ complexes from exo-2-oxazolidinone dienes. A facile generation of stable conjugated enol-enamido species

A synthesis of new η⁴ -diene-Fe(CO)₃ complexes derived from the novel exo-2-oxazolidinone dienes is described. These complexes were prepared by thermal complexation of the substituted dienes with diiron nonacarbonyl to afford the corresponding complexes as crystal solids. The X-ray single-crystal structure analysis revealed characteristic structural properties for diene-iron complexes, showing that in the conformation of the distorted trigonal-pyramidal geometry two of the carbonyl groups point out from the metal toward the vertex C4 and C5 atoms of the heterocycle. Unsuccessful functionalization of the diene moiety by acylation or alkylation of the allylic position indicated the strong stability of these dienes. This stability facilitated the generation of stable and unprecedented conjugated enamine-enol ester- and enamido-enol-Fe(CO)₃ complexes, by either kinetic or themodynamic control of the reaction conditions.