We have used extensively ironbicarbonyl lactone and lactic complexes as a conceptually new bond forming process to lactones, lactams.  These complexes also served as key entry points to 1,5 and 1,7 remote control and as precursors to various natural products.  

See π-Allyltricarbonyliron lactone complexes in organic synthesis: a useful and conceptually unusual route to lactones and lactams S.V. Ley, L.R. Cox, G. Meek, Chem. Rev199696, 423-442.

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