Abstract
Enantioselective organocatalysis has become a field of central importance within asymmetric chemical synthesis and appears to be efficient approach toward the construction of complex chiral molecules from simple achiral materials in one-pot transformations under mild conditions with high stereocontrol. This review addresses the most significant synthetic methods reported on chiral-amine-catalyzed tandem Michael conjugate addition of heteroatom-centered nucleophiles to α,β-unsaturated compounds followed by cyclization reactions for the enantioselective construction of functionalized chiral chromenes, thiochromenes and 1,2-dihydroquinolines in optically enriched forms found in a myriad of bioactive natural products and synthetic compounds.
Highlights
Chromenes or benzopyrans and their sulfur and nitrogen analogues are important classes of structural motifs found in numerous naturally occurring and synthetic compounds
In this review we have summarized our efforts to cover various chiralamine-catalyzed synthetic protocols leading to one-pot enantioselective synthesis of six membered mono hetero-atom containing, biologically active heterocycles, such as functionalized chromenes, thiochromenes and 1,2-dihydroquinolines, by means of tandem/domino hetero Michael addition reactions, or modified versions [33,34,35,36,37,38], covering the literature up to 2011
With benzoic acid as cocatalyst and dichloroethane as solvent, the test reaction provided the chiral chromenes 3 in good yields and enantioselectivities (99%) at room temperature (Scheme 3)
Summary
Chromenes or benzopyrans and their sulfur and nitrogen analogues are important classes of structural motifs found in numerous naturally occurring and synthetic compounds. Organocatalytic tandem Michael conjugate additions of heteroatom-centered nucleophiles to α,β-unsaturated compounds appear as one of the most reliable and powerful tools for the stereocontrolled access to a wide range of biologically active heterocycles in optically enriched form [29,30,31,32]. In this review we have summarized our efforts to cover various chiralamine-catalyzed synthetic protocols leading to one-pot enantioselective synthesis of six membered mono hetero-atom containing, biologically active heterocycles, such as functionalized chromenes (benzopyranes), thiochromenes (thiobenzopyranes) and 1,2-dihydroquinolines, by means of tandem/domino hetero Michael addition reactions, or modified versions [33,34,35,36,37,38], covering the literature up to 2011. The initial screening result of various organocatalysts with their percentage of conversion (% yield) and enantiomeric excess (ee) is presented in tabular form, and the best catalyst is used for the given individual scheme
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