Organocatalytic asymmetric formal oxidative coupling for the construction of all-aryl quaternary stereocenters

Abstract

A new catalytic asymmetric formal cross dehydrogenative coupling process for the construction of all-aryl quaternary stereocenters is disclosed, which provides access to the rarely explored chiral tetraarylmethanes with excellent enantioselectivity....

Enantioselective construction of triaryl-substituted all-carbon quaternary stereocenters via organocatalytic arylation of oxindoles with azonaphthalenes

“…A more challenging scenario arises when the stereocenters contain triaryl-substitution, where the subtle difference between the three arene substituents could hinder stereodifferentiation. 5,6 Therefore, straightforward routes to prepare specifically functionalized frameworks with triaryl-substituted all-carbon quaternary stereocenters are always desirable. 5,6 The unique electronic nature of ortho - or para -quinone methides 7 renders a convenient platform to forge such carbon centers by means of bifunctional chiral phosphoric acid (CPA) catalysis.…”

“…5,6 Therefore, straightforward routes to prepare specifically functionalized frameworks with triaryl-substituted all-carbon quaternary stereocenters are always desirable. 5,6 The unique electronic nature of ortho - or para -quinone methides 7 renders a convenient platform to forge such carbon centers by means of bifunctional chiral phosphoric acid (CPA) catalysis. 8 A series of pioneering contributions have been made by the Sun group in utilizing racemic tertiary alcohols or 1,1-diarylethylenes as the precursors for ortho - or para -quinone methides in various heteroarylation reactions (Scheme 1a).…”

“… 8 A series of pioneering contributions have been made by the Sun group in utilizing racemic tertiary alcohols or 1,1-diarylethylenes as the precursors for ortho - or para -quinone methides in various heteroarylation reactions ( Scheme 1a ). 5 In Liu's protocol, racemic 2,2-diarylacetonitriles were used for enantioselective oxidative cross-coupling with (hetero)arenes ( Scheme 1b ). 6 Despite the robustness of these routes, an ortho - or para -hydroxyl group should be installed at one of the aromatic rings in the diaryl substrates for in situ generation of the reactive quinone methide intermediates.…”

Brønsted acid-catalyzed C6 functionalization of 2,3-disubstituted indoles for construction of cyano-substituted all-carbon quaternary centers

“…δ , δ -Disubstituted para -quinone methides ( p -QMs) have been recognized as important synthons for the formation of all-carbon quaternary centers owing to the intrinsically strong electrophilic characteristics. 7–11 The approaches to generate δ , δ -disubstituted p -QMs include Brønsted acid-catalyzed dehydration of p -hydroxybenzyl alcohols 8,9 and oxidant mediated C–H oxidation of diarylmethanes bearing electron-withdrawing groups. 10,11 b Owing to our interest in C6 functionalization of 2,3-disubstituted indoles, 3 d ,12 we conceived the catalytic direct C6 functionalization of 2,3-disubstituted indoles with δ , δ -disubstituted p -QMs which were in situ generated from 2,2-diarylacetonitriles under oxidative conditions.…”

“…7–11 The approaches to generate δ , δ -disubstituted p -QMs include Brønsted acid-catalyzed dehydration of p -hydroxybenzyl alcohols 8,9 and oxidant mediated C–H oxidation of diarylmethanes bearing electron-withdrawing groups. 10,11 b Owing to our interest in C6 functionalization of 2,3-disubstituted indoles, 3 d ,12 we conceived the catalytic direct C6 functionalization of 2,3-disubstituted indoles with δ , δ -disubstituted p -QMs which were in situ generated from 2,2-diarylacetonitriles under oxidative conditions. The electron-withdrawing cyano group of 2,2-diarylacetonitrile would tune the molecular electron-density distribution, and the stability of the resulting p -QMs might be enhanced by reducing their polymerizability.…”