Chiral Anion Catalysis in the Enantioselective 1,4-Reduction of the 1-Benzopyrylium Ion as a Reactive Intermediate
作者:Masahiro Terada、Takuto Yamanaka、Yasunori Toda
DOI:10.1002/chem.201302486
日期:2013.10.4
Anionic! Novel chiral anion catalysis of the enantioselective 1,4‐reduction of the 1‐benzopyrylium ion by a chiral phosphoric acid was accomplished with a Hantzsch ester as the reducing agent. The enantioselective reduction established is composed of a two‐step consecutive transformation involving stereoablative loss of the hydroxy group from racemic 2H‐chromen‐2‐ol derivatives to generate the achiral
阴离子!以Hantzsch酯为还原剂,完成了手性磷酸对1-苯并吡啶离子对映体1,4-还原的新型手性阴离子催化。建立的对映选择性还原包括两步连续转化,其中涉及从消旋的2 H - chromen -2-ol衍生物中羟基的立体烧蚀损失,生成非手性的1-benzopyrylium离子作为反应性关键中间体。
Rhodium‐Catalysed Asymmetric Synthesis of 4‐Alkyl‐4
<i>H</i>
‐Chromenes
作者:Zhiqian Chang、Jian Yao、Xiaowei Dou
DOI:10.1002/adsc.202000579
日期:2020.9.8
A general method for the catalyticasymmetricsynthesis of 4‐alkyl‐4H‐chromenes was developed. With readily available β‐alkyl‐substituted enones and 2‐hydroxylated arylboronic acids, a rhodium‐catalysed asymmetric conjugate addition/intramolecular hemi‐acetalization/acid‐promoted dehydration sequence leads to the formation of 4‐alkyl‐4H‐chromenes in up to 99% yield and with up to >99% ee. The current
A generalmethod to access diverse chiral phenols by rhodium-catalyzed asymmetric conjugate arylation using hydroxylated arylboronic acids in ethanol was developed. Recycling of the rhodium catalyst by flash chromatography on silica gel was feasible in this system. The synthetic utility of the strategy was demonstrated by efficient synthesis of chiral drug tolterodine.
A new light‐driven asymmetricion‐pair catalysis procedure for the metal‐free enantioselectivehydrogenation of in situ generated pyryliumions from readily available chalcones was developed (see scheme). The photo‐assisted Brønsted acid catalyzed procedure has broad scope and allows, for the first time, access to valuable 4H‐chromenes in good yields and with excellent enantioselectivities.
Enantioselective Decarboxylative Alkylation of β-Keto Acids to <i>ortho</i>-Quinone Methides as Reactive Intermediates: Asymmetric Synthesis of 2,4-Diaryl-1-benzopyrans
作者:Hyun Jung Jeong、Dae Young Kim
DOI:10.1021/acs.orglett.8b00993
日期:2018.5.18
efficient asymmetric synthesis of 2,4-diaryl-1-benzopyrans via enantioselective decarboxylative alkylation of β-keto acids to o-QM intermediates, followed by sequential cyclization and dehydration, has been developed. The synthetically useful chiral 2,4-diaryl-1-benzopyran derivatives were obtained in moderate to high yields and high enantioselectivities through a one-pot, two-step sequence. This approach