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Enantioselective Synthesis of trans-1-Alkyl-
T. den Hartog, A. Rudolph, B. Maciá, A. J. Minnaard*, B. L. Feringa*
University of Groningen, The Netherlands
21 December 2010 (online)
The asymmetric synthesis of trans-1-alkyl-2-substituted cyclopropanes has traditionally been based on the well-known Simmons-Smith cyclopropanation. However, a stoichiometric amount of a chiral dioxaborolane is needed and efficient catalytic methods are very rare. The authors represent a catalytic asymmetric tandem conjugate addition-intramolecular enolate trapping reaction by using the Cu-TolBINAP complex. Reactions of various Grignard reagents to 4-Cl-α,β-unsaturated esters, thioesters, and ketones provide highly functionalized cyclopropanes in excellent yields and enantioselectivities.