Catalytic Enantioselective [3 + 2] Cycloaddition of α-Keto Ester Enolates and Nitrile Oxides
作者:Samuel L. Bartlett、Yoshihiro Sohtome、Daisuke Hashizume、Peter S. White、Miki Sawamura、Jeffrey S. Johnson、Mikiko Sodeoka
DOI:10.1021/jacs.7b03782
日期:2017.6.28
An enantioselective [3 + 2] cycloaddition reaction between nitrileoxides and transiently generated enolates of α-keto esters has been developed. The catalyst system was found to be compatible with in situ nitrile oxide-generation conditions. A versatile array of nitrileoxides and α-keto esters could participate in the cycloaddition, providing novel 5-hydroxy-2-isoxazolines in high chemical yield
Reaction design in asymmetric catalysis has traditionally been predicated on a structurally robust scaffold in both substrates and catalysts, to reduce the number of possible diastereomeric transition states. Herein, we present the stereochemical dynamics in the Ni(II)-catalyzed diastereoconvergent (3 + 2) cycloadditions of isomerizable nitrile-conjugated nitrones with α-ketoesterenolates. Even in
Asymmetric Hetero-Diels–Alder Reaction of Danishefsky’s Dienes with α-Carbonyl Esters Catalyzed by an Indium(III)–PyBox Complex
作者:Bei Zhao、Teck-Peng Loh
DOI:10.1021/ol400841s
日期:2013.6.21
An efficient catalytic enantioselective hetero-Diels–Alderreaction of Danishefsky’s dienes with α-carbonyl esters using a chiral In(III)–pybox complex has been demonstrated. This protocol offers several advantages, including mildreaction conditions, relatively low catalyst loading, and good to excellent enantioselectivities. Furthermore, the absolute configurations of the new alkynyl-containing products
provided allenoates, tetrasubstituted α,γ-dihaloallenoates, and functionalized tricyclic azepines. A reaction of alkynyl hydrazones with N-halosuccinimides captures the electrophile in 2-fold that delivers fully substituted dibromo- and diiodoallenoates in good yields. In addition, a DABCO-promoted Wolff–Kishner reduction of hydrazones, followed by isomerization, provides versatile allenoates under mild conditions
A highly practical and stereoselective route to 1,4-dicarbonyl 2,3-dihaloalkenes is presented. The strategy involves bench-stable unprotected alkynyl hydrazones and commercially available N-halosuccinimides that provide γ-oxo-α,β-(Z)-dihaloenoates in excellent yields with complete Z-selectivity. The protocol also furnishes vicinal dihaloalkenes with two different halogen atoms. Also, a straightforward
提出了一种高度实用且立体选择性的 1,4-二羰基 2,3-二卤代烯烃合成路线。该策略涉及实验室稳定的未保护的炔基腙和市售的N -卤代琥珀酰亚胺,它们以优异的收率提供具有完全Z选择性的 γ-氧代-α,β-( Z )-二卤代烯酸酯。该方案还提供了具有两个不同卤素原子的邻位二卤代烯烃。此外,还证明了从容易获得的 2-氧代-3-丁酸中直接一锅法合成二卤代烯酸。此外,还探索了 4-oxo-2,3-dibromoenoates 的潜在合成转化,其中包括有价值的五元和六元杂环的合成。