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DOI: 10.1055/s-2008-1042722
Organocatalytic Oxy-Michael Addition
Contributor(s):Benjamin List, Subhas Chandra PanUniversity of Texas Southwestern Medical Center, Dallas, USA
Enantioselective, Organocatalytic Oxy-Michael Addition to γ/δ-Hydroxy-α,β-enones: Boronate-Amine Complexes as Chiral Hydroxide Synthons
J. Am. Chem. Soc. 2008, 130: 46-48
Publication History
Publication Date:
21 February 2008 (online)
Key words
oxy-Michael addition - γ/δ-hydroxy-α,β-enones - bifunctional thioureas - enantioselectivity
Significance
The authors report an enantioselective organocatalytic oxy-Michael addition to γ/δ-hydroxy-α,β-unsaturated ketones 1 and 2. Bifunctional thiourea catalysts 5 or 6 in combination with PhB(OH)2 were found to be effective for the reaction. After basic H2O2 workup, chiral diols 3 and 4 were obtained from the dioxaborolane intermediates. While catalyst 5 was the best catalyst for the γ-hydroxy-α,β-enones, catalyst 6 was found to be highly enantioselective for δ-hydroxy-α,β-enones. With 10-20 mol% of the catalysts, good to high yields (71-95%) and excellent enantioselectivities (er = 94:6 to >99:1) are obtained for different enones.
Comment
Watanabe and co-workers have earlier reported an asymmetric oxy-Michael addition to γ/δ-hydroxy-α,β-unsaturated ketones utilizing chiral hemiketals derived from d-glucose (Chirality 2001, 13, 379). The present authors have developed an unprecedented catalytic asymmetric approach where an amine-boronate complex acts as chiral synthon. The authors have also shown the utility of their reaction products in natural product synthesis.