Asymmetric Cycloaddition of β,γ-Unsaturated α-Ketoesters with Electron-Rich Alkenes Catalyzed by a Chiral Er(OTf)3/N,N′-Dioxide Complex: Highly Enantioselective Synthesis of 3,4-Dihydro-2 H-pyrans
The asymmetric inverse‐electron‐demand hetero‐Diels–Alder (HDA) reactions of β,γ‐unsaturated α‐ketoesters with electron‐rich alkenes were investigated, with an N,N′‐dioxide/erbium(III) complex employed as the catalyst. Quantitative conversion of the β,γ‐unsaturated α‐ketoesters and excellent enantioselectivities (up to >99 % ee) and diastereoselectivities (up to >99:1 d.r.) were observed for a broad
Valuable substrates for the synthesis of natural products, compounds 3 (R1 =alkyl, aryl, alkoxy; R2 , R3 =alkyl) are formed from β,γ-unsaturated α-keto esters 1 and vinyl ethers 2 by the title reaction [Eq. (1)]. Copper(II) bisoxazolines act as catalysts, and in many cases enantiomeric excesses higher than 99.5 % are achieved.
A Novel Catalytic and Highly Enantioselective Approach for the Synthesis of Optically Active Carbohydrate Derivatives
作者:Hélène Audrain、Jacob Thorhauge、Rita G. Hazell、Karl Anker Jørgensen
DOI:10.1021/jo9918596
日期:2000.7.1
yield, high diastereoselectivity, and excellent enantioselectivity. The potential of the reaction is demonstrated by the synthesis of optically active carbohydrates such as spiro-carbohydrates, an ethyl beta-D-mannoside tetraacetate, and acetal-protected C-2-branched carbohydrates. On the basis of X-ray crystallographic data and the absolute configuration of the products, it is proposed that the alkene