Chiral phosphine–phosphite ligands in the enantioselective 1,4-addition of Grignard reagents to α,β-unsaturated carbonyl compounds

A library of chiral phosphine–phosphite ligands was evaluated in the Cu-catalyzed asymmetric 1,4-addition of Grignard reagents to cyclopentenone, cycloheptenone and 5,6-dihydro-2 H-pyran-2-one. TADDOL-based ligands 1a and 1b with a bulky substituent at the ortho-position to the chiral phosphite moie...

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Bibliographic Details
Published in:Tetrahedron: asymmetry 2011-04, Vol.22 (8), p.887-892
Main Authors: Naeemi, Qaseem, Robert, Tobias, Kranz, Darius P., Velder, Janna, Schmalz, Hans-Günther
Format: Article
Language:English
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Summary:A library of chiral phosphine–phosphite ligands was evaluated in the Cu-catalyzed asymmetric 1,4-addition of Grignard reagents to cyclopentenone, cycloheptenone and 5,6-dihydro-2 H-pyran-2-one. TADDOL-based ligands 1a and 1b with a bulky substituent at the ortho-position to the chiral phosphite moiety gave rise to the 1,4-addition products with high enantioselectivities (up to 93% ee). In addition to ethyl-MgBr (as a standard alkyl nucleophile) phenyl- and isopropenyl-MgBr could also be employed. In the case of cyclopentenone, the use of chlorotrimethylsilane as an additive led to improved regio- and enantioselectivities.
ISSN:0957-4166
1362-511X
DOI:10.1016/j.tetasy.2011.04.018