Correlation of rates of uncatalyzed and hydroxide-ion catalyzed ketene hydration. A mechanistic application and solvent isotope effects on the uncatalyzed reaction
Forming All‐Carbon Quaternary Stereocenters by Organocatalytic Aminomethylation: Concise Access to β
<sup>2,2</sup>
‐Amino Acids
作者:Kai Wang、Jianliang Yu、Ying Shao、Shengbiao Tang、Jiangtao Sun
DOI:10.1002/anie.202009892
日期:2020.12.21
The asymmetric synthesis of β2,2‐amino acids remains a formidable challenge in organic synthesis. Here a novel organocatalytic enantioselective aminomethylation of ketenes with stable and readily available N,O‐acetals is reported, providing β2,2‐amino esters bearing an all‐carbonquaternarystereogenic center in high enantiomeric ratios with a catalytic amount of chiral phosphoric acid. Typically,
Lewis Acid-Promoted Ketene–Alkene [2 + 2] Cycloadditions
作者:Christopher M. Rasik、M. Kevin Brown
DOI:10.1021/ja3103007
日期:2013.2.6
are the first examples of ketene-alkene [2 + 2] cycloadditions promoted by Lewis acids. Notable features of this method include (1) substantial rate acceleration relative to traditional thermal reactions, (2) good diastereoselectivities and yields for the formation of the cyclobutanone products, and (3) inverse diastereoselectivity compared with related thermal cycloadditions for many examples. These
difluoroenoxysilanes is disclosed for the first time, which enabled the direct construction of versatile gem-difluoroalkenes through an unprecedented highly efficient addition reaction with ketenes. A series of valuable gem-difluoroenol esters were achieved in good to excellent yields. The synthetic versatility of this protocol is further demonstrated by the gram-scale synthesis and good functional group tolerance
Asymmetric Pericyclic Cascade Approach to Spirocyclic Oxindoles
作者:Edward Richmond、Nicolas Duguet、Alexandra M. Z. Slawin、Tomáš Lébl、Andrew D. Smith
DOI:10.1021/ol300982f
日期:2012.6.1
The reaction of chiral N-arylnitrones with carbocyclic alkylarylketenes generates spirocyclic oxindoles in good yields and with excellent levels of enantioselectivity (90-99% ee) via a pericyclic cascade process.
Enantioselective protonation of samarium enolates by a C2-symmetric chiral diol
High enantioselectivity (up to 97%ee) have been achieved in the protonation of samarium enolates which were generated by SmI2-mediated cross-coupling reaction between unsymmtrical dialkylketene and allyl iodide, using a C-2-symmetric chiral diol as a proton source. The stereochemistry of enolate formation and of the enantioselective protonation is discussed.