Helical chirality and selective anion-binding processes are key strategies used in nature to promote highly enantioselective chemical reactions. Although enormous efforts have been made to develop simple helical chiral systems and thus open new possibilities in asymmetric catalysis and synthesis, the efficient use of synthetic oligo- and polymeric helical chiral catalysts is still very challenging and rather unusual. In this work, structural unique chiral oligotriazoles have been developed as C-H bond-based anion-binding catalysts for the asymmetric dearomatization of N-heteroarenes. These rotational flexible catalysts adopt a reinforced chiral helical conformation upon binding to a chloride anion, allowing high levels of chirality transfer via a close chiral anion-pair complex with a preformed ionic substrate. This methodology offers a straightforward and potent entry to the synthesis of chiral (bioactive)heterocycles with added synthetic value from simple and abundant heteroarenes.
Loving getting in touch: The use of the high affinity of certain small organic molecules to anions for the development of acceptor catalysis is discussed. Covered in particular, are reactions that imply the activation of ionic electrophiles by H‐bonding to their counter anions.
Easily accessible and tunable chiral triazoles have been introduced as a novel class of C-H bond-based H-donors for anion-binding organocatalysis. They have proven to be effective catalysts for the dearomatization reaction of different N-heteroarenes. Although this dearomatization approach represents a powerful strategy to build chiral heterocycles, to date only a few catalytic methods to this end exist. In this work, the organocatalyzed enantioselective Reissert-type dearomatization of isoquinoline derivatives employing a number of structurally diverse chiral triazoles as anion-binding catalysts was realized. The here presented method was employed to synthesize a number of chiral 1,2-dihydroisoquinoline substrates with an enantioselectivity up to 86:14 e.r. Moreover, a thorough study of the determining parameters affecting the activity of this type of anion- binding catalysts was carried out.
A new player on the field! “Click” bis‐triazoles have been introduced as a highly efficient new class of neutral CH⋅⋅⋅anion‐binding organocatalysts (see scheme). DFT and NMR studies were used to confirm this activation modus and identify the optimal catalyst.
Kumada-Corriu cross-couplings of nonactivated cyclic and acyclic vinyl phosphates with aryl magnesium reagents afforded a series of 1,1-disubtituted alkenes in good yields for most cases when the reactions were performed at room temperature with the simple palladium salt, PdCl(2), without the presence of phosphine ligands.
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