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On the Mechanism of the Copper-Catalyzed Cyclopropanation Reaction

✍ Scribed by Torben Rasmussen; Jakob F. Jensen; Niels Østergaard; David Tanner; Tom Ziegler; Per-Ola Norrby

Publisher
John Wiley and Sons
Year
2002
Tongue
English
Weight
235 KB
Volume
8
Category
Article
ISSN
0947-6539

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✦ Synopsis

The selectivity-determining step in enantioselective copper-catalyzed cyclopropanation with diazo compounds has been studied by experimental and computational methods. The addition of the very reactive metallacarbene intermediate in an early transition state to the substrate alkene is concerted but strongly asynchronous, with substantial cationic character on one alkene carbon in the neighborhood of the transition state. Evidence from isotope effects and Hammett studies supports the nature of the transition state. Formation of a metallacyclobutane intermediate by a [2+2] addition is kinetically disfavored. Ligand-substrate interactions influencing the enantio- and diastereoselectivity have been identified, and the preferred orientation of the alkene substrate during the addition is suggested.

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