Asymmetric Synthesis of 1,3-Dioxolanes by Organocatalytic Formal [3 + 2] Cycloaddition via Hemiacetal Intermediates
作者:Keisuke Asano、Seijiro Matsubara
DOI:10.1021/ol3003755
日期:2012.3.16
A novel asymmetricformal [3 + 2] cycloaddition reaction for the synthesis of 1,3-dioxolanes using cinchona-alkaloid-thiourea-based bifunctional organocatalysts is reported. The reaction proceeds via the formation of hemiacetal intermediates between γ-hydroxy-α,β-unsaturated ketones and aldehydes.
Highly Efficient Asymmetric Additions of Diethylzinc to Aldehydes Triply Activated by Chiral Phosphoramide-Zn(II) Complexes Derived From Cinchona Alkaloids
作者:Bin Shen、Huayin Huang、Guangling Bian、Hua Zong、Ling Song
DOI:10.1002/chir.22171
日期:2013.9
New chiral phosphoramide ligands derived from cinchona alkaloids were developed, which react with diethylzinc to form chiral phosphoramide‐Zn(II) complexes containing two Lewis bases and one Lewis acid. These trifunctional complexes can serve as highly efficient chiral catalysts for triple activation of enantioselective addition reactions of diethylzinc with aldehydes to give desired alcohol products
Asymmetric Catalytic Cycloetherification Mediated by Bifunctional Organocatalysts
作者:Keisuke Asano、Seijiro Matsubara
DOI:10.1021/ja207322d
日期:2011.10.26
Oxacyclic structures such as tetrahydrofuran (THF) rings are commonly found in many bioactive compounds, and this has led to several efforts toward their stereoselective syntheses. However, the process of catalytic asymmetric cycloetherification for their straightforward synthesis has remained a challenge. In this study, we demonstrate a novel asymmetric synthesis method for THF via the catalytic cycloetherification of epsilon-hydroxy-alpha,beta-unsaturated ketones mediated by cinchona-alkaloid-thiourea-based bifunctional organocatalysts. This catalytic process represents a highly practical cycloetherification method that provides excellent enantioselectivities, even with low catalyst loadings at ambient temperature.
Asymmetric Oxy-Michael Addition to γ-Hydroxy-α,β-Unsaturated Carbonyls Using Formaldehyde as an Oxygen-Centered Nucleophile
Formaldehyde was utilized as an oxygen-centered nucleophile in an asymmetric oxy-Michael addition to gamma-hydroxy-alpha,beta-unsaturated carbonyl compounds using bifunctional organocatalysts through hemiacetal intermediates. The cyclic acetal product could be further transformed into beta-hydroxycarbonyl compounds, useful synthetic intermediates leading to various important target molecules. As such, this method is an example of a novel formal asymmetric hydration of alpha,beta-unsaturated carbonyl compounds.