A catalytic
asymmetric direct C–H arylation of (η6-arene)chromium
complexes to obtain planar-chiral compounds
is reported. The use of the hemilabile ligand H8-BINAP(O)
is key to providing high enantioselectivity in this transformation.
We show that this methodology opens the door to the synthesis of a
variety of planar-chiral chromium derivatives which can be easily
transformed into planar chiral mono- or diphosphines. Mechanistic
studies, including synthesis and characterization of Pd and Ag complexes
and their detection in the reaction mixture, suggest a Pd-catalyzed/Ag-promoted
catalytic system where Ag carries out the C–H activation step.
The highly enantioselective asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates with anthrones is presented. The reaction is simply catalyzed by cinchona alkaloid derivatives affording the final alkylated products in good yields and excellent enantioselectivities.
Novel (thio)urea-tertiary phosphines were developed for use as bifunctional organocatalysts readily available from naturally occurring molecules: saccharides and amino acids. The efficiency of the organocatalysts was demonstrated in the asymmetric Morita-Baylis-Hillman (MBH) reaction of aromatic aldehydes with acrylates. The MBH products were obtained in good yields (up to 85%) and with high enantioselectivities (up to 87% ee).
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