The catalysis of Michael reactions by FeCl₃ · 6 H₂O is an environmentally sound alternative to classical base catalysis [1]. A number of β-diketones and β-oxo esters are cleanly converted with methyl vinyl ketone to the corresponding Michael reaction products within a few hours at ambient temperature with quantitative yields being achieved in most cases. The reaction can be performed solvent free and without any need for anhydrous or inert condi­tions. Due to quantitative chemoselectivity, work-up and purification are very simple. Iron com­pounds are readily available, and with respect to economical and environmental considerations, it is the transition metal catalyst of choice. Starting materials are converted stoichio­metrically and atom-economically without any need of reagents or even solvents and without generation of any by-product.

We have investigated the mechanism of this process by X-ray absorption and Raman spectroscopy [2], ESI-MS spectrometry as well as kinetic studies and DFT-calculations [3]. Actually, a strong anion-dependence of the catalytic activity was predicted by our spectro­scopic and theoretical studies which led to the development of a new catalyst system being about 10 times more active than FeCl₃ · 6 H₂O.

[1] a) J. Christoffers, Chem. Comm. 1997, 943-944. b) J. Christoffers, Org. Synth. 2000, 78, 249-253. c) Review: J. Christoffers, Synlett 2001, 723-732.

[2] M. Bauer, T. Kauf, J. Christoffers, H. Bertagnolli, Phys. Chem. Chem. Phys. 2005, 7, 2664-2670.

[3] S. Pelzer, T. Kauf, C. van Wüllen, J. Christoffers, J. Organomet. Chem. 2003, 684, 308-314.

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