Highly Diastereoselective Cyclopropanation of Olefins Catalysed By a C2-Symmetrical Chiral Iron Porphyrin Complex

Compounds containing cyclopropane units play a crucial role in both synthetic and pharmaceutical chemistry due to high reactivity and biological properties of the three-membered ring.[1] Consequently, the interest of the research community in developing new methodologies to synthesise cyclopropanes is strongly increasing. Amongst the synthetic procedures available, the one-pot reaction of diazo compounds with olefins is a sustainable and atom-efficient strategy due to the formation of N₂as the only stoichiometric by product.

Catalytic enantio- and diasteroselective olefin cyclopropanations [2] have been extensively explored and metal porphyrin complexes represent a very active and stereoselective class of catalysts. Some years ago we reported on the catalytic efficiency of chiral cobalt(II)-binaphthyl porphyrins in asymmetric cyclopropanations, [3] and recorded positive data encouraging us to synthesise the structurally related chiral porphyrin 1 and its iron(III) complex 2 (see figure). The catalytic activity of 2 in the asymmetric cyclopropanation of olefins by diazo compounds was investigated. Cyclopropanes were obtained with excellent yields (up to 99%), enantio- and diasteroselectivities (ee_trans up to 80%, cis/trans ratios up to 99%). In addition to that, outstanding values of TON and TOF (20,000 and 120,000/h respectively) were achieved. [4]

References

[1] A. K. Kumar, Intern. J. Pharm. and Pharm. Sci. 2013, 5, 467-472.

[2] D. Intrieri, A. Caselli and E. Gallo, Eur. J. Inorg. Chem. 2011, 5071-5081.

[3] (a) S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini and S. Cenini, Organometallics, 2008, 27, 6143-6151. (b) A. Penoni, R. Wanke, S. Tollari, E. Gallo, D. Musella, F. Ragaini, F. Demartin and S. Cenini, Eur. J. Inorg. Chem. 2003, 1452-1460.

[4] D. Intrieri, S. Le Gac, A. Caselli, E. Rose, B. Boitrel and E. Gallo submitted