Axially chiral indole-based frameworks have been recognized as ac lass of important five-membered heterobiaryls andd eveloping catalytic asymmetric approaches for constructingt hese frameworks in an enantioselective manner is highly desirable. In recent years, syntheticc hemists have paid much attention to this research field, and rapid developments have occurred. At this point, ar ange of axially chiral indole-based scaffolds have been constructed via various catalytic asymmetric reactions based on different strategies. Thus, the catalytic asymmetric construction of axially chiral indole-based frameworks has becomea ne merging area. This minireview summarizes the rapid advances in this field and gives some insights into future developments, which will help this research field to thrive.
Chiral indole derivatives such as indolines and indolenines are important heterocyclic frameworks which constitute the core structures of many natural products and bioactive molecules. So, intensive attentions from chemists have...
Atroposelective
synthesis of axially chiral molecules has attracted
substantial attention from chemists because of the importance of such
molecules. However, catalytic asymmetric synthesis of axially chiral
styrenes or vinyl arenes is underdeveloped and challenging due to
the low rotational barrier and weak configurational stability of such
molecules. Therefore, the development of powerful strategies for the
catalytic atroposelective synthesis of axially chiral styrenes or
vinyl arenes is of great importance. In this work, we have accomplished
the first atroposelective access to oxindole-based axially chiral
styrenes by the strategy of catalytic kinetic resolution, and this
strategy offered two kinds of oxindole-based axially chiral styrene
derivatives in good diastereoselectivities (up to 94:6 dr) and excellent
enantioselectivities (up to 98% ee) with high selectivity factors
(S up to 106). This strategy not only provides easy
access to oxindole-based axially chiral styrenes but also offers a
robust method for synthesizing bisamide derivatives bearing both axial
and central chirality. More importantly, this strategy has added a
new class of members to the atropisomeric family, especially to the
family of axially chiral styrenes.
The regio‐ and enantioselective (3+3) cycloaddition of nitrones with 2‐indolylmethanols was accomplished by the cooperative catalysis of hexafluoroisopropanol (HFIP) and chiral phosphoric acid (CPA). Using this approach, a series of indole‐fused six‐membered heterocycles were synthesized in high yields (up to 98 %), with excellent enantioselectivities (up to 96 % ee) and exclusive regiospecificity. This approach enabled not only the first organocatalytic asymmetric (3+3) cycloaddition of nitrones but also the first C3‐nucleophilic asymmetric (3+3) cycloaddition of 2‐indolylmethanols. More importantly, theoretical calculations elucidated the role of the cocatalyst HFIP in helping CPA control the reactivity and enantioselectivity of the reaction, demonstrating a new mode of cooperative catalysis.
A copper-catalyzed condensation reaction of oxime acetates and α,β-unsaturated ketimines to give pyridine derivatives is reported. The reaction features mild conditions, high functional-group compatibility, and high regioselectivity with respect to unsymmetrical oxime acetates, thus allowing the preparation of a wide range of polysubstituted pyridines, many of which are not readily accessible by conventional condensation methods.
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