Discovery and Application of Doubly Quaternized Cinchona‐Alkaloid‐Based Phase‐Transfer Catalysts

Abstract

We report the discovery of novel N,N'-disubstituted cinchona alkaloids as efficient phase-transfer catalysts for the assembly of stereogenic quaternary centers. In comparison to traditional cinchona-alkaloid-based phase-transfer catalysts, these new catalysts afford substantial improvements in enantioselectivity and reaction rate for intramolecular spirocyclization reactions with catalyst loadings as low as 0.3 mol% under mild conditions.

Modulation of charge transfer by N-alkylation to control photoluminescence energy and quantum yield

“…29,30 This selectivity follows the known basicity trend of N1 and N2. 21,31,32 Methylation at each site gives characteristic changes in 1 H NMR chemical shis ( Fig. S14 and S15 †) and is conrmed by X-ray diffraction (XRD) analysis of single crystals (Scheme 1).…”

Phosphonium Salts in Asymmetric Catalysis: A Journey in a Decade's Extensive Research Work

“…Furthermore, Zhao and co‐workers used multifunctional catalyst to synthesize a spirocyclic oxindole scaffold, a basic structural core for a number of alkaloids including Citrinadin B, Cyclopiamine B, Notamide and Paraherquamide F (Figure ). The basic core of these spirocyclic oxindoles could be obtained by reacting N ‐benzyl‐protected methyleneindolinone 163 and γ‐malonate‐substituted α,β‐unsaturated ester 164 in the presence of multifunctional phosphonium salts under phase‐transfer condition, in addition to the previously reported methods –. In this transformation as well, the use of bifunctional catalysts displayed excellent yields (>96%), but with moderate ee s (<71%).…”

Squaramide‐Catalyzed Synthesis of Enantioenriched Spirocyclic Oxindoles via Ketimine Intermediates with Multiple Active Sites

“…[1] In particular, enantiopure five-membered spirocyclic oxindoles have attracted tremendous attention owing to their diverse bioactivities and structural complexity.T he key challenge for the construction of such structures lies in the formation of multiple stereocenters,p articularly for those containing two adjacent quaternary centers.T herefore,n ew strategies for the synthesis of such spirocyclic oxindoles [2] with high levels of efficiency and selectivity from readily available starting materials are always in great demand.In the past few years,elegant advances have been made in the development of enantioselective syntheses of five-membered spirocyclic oxindoles. [3] In 2007, Tr ost [4] and co-workers disclosed ap alladium-catalyzed [3+ +2] cycloaddition for the assembly of such compounds.A side from transition-metal catalysis,o rganocatalytic cascade reactions provide an alternative powerful strategy for the preparation of spirocyclic oxindoles.A fter [3+ +2] cycloadditions catalyzed by chiral tertiary phosphines [5] or amines [6] had been reported, hydrogen bond donor catalyzed cascade reactions, [7] Michael-Michael reactions promoted by primary [8] or secondary amines, [9] NHC-catalyzed processes, [10] as well as alkylations mediated by phase transfer catalysts (PTCs) [11] were developed. More recently,s ynergistic catalysis [12] and CÀHb ond oxygenation [13] were also applied to the asymmetric construction of five-membered spirocyclico xindoles.Inspired by our ongoing interest in the development of reactions towards spirocyclico xindoles [14] and previous work on nitrosoarenes, [15] we hypothesized that the addition of b-dicarbonyl compounds to nitrosoarenes followed by aMichael-Mannich sequence in the presence of abifunctional catalyst would be an appropriate strategy to prepare enantioenriched spirocyclico xindoles (Scheme 1d).…”

“…In the past few years,elegant advances have been made in the development of enantioselective syntheses of five-membered spirocyclic oxindoles. [3] In 2007, Tr ost [4] and co-workers disclosed ap alladium-catalyzed [3+ +2] cycloaddition for the assembly of such compounds.A side from transition-metal catalysis,o rganocatalytic cascade reactions provide an alternative powerful strategy for the preparation of spirocyclic oxindoles.A fter [3+ +2] cycloadditions catalyzed by chiral tertiary phosphines [5] or amines [6] had been reported, hydrogen bond donor catalyzed cascade reactions, [7] Michael-Michael reactions promoted by primary [8] or secondary amines, [9] NHC-catalyzed processes, [10] as well as alkylations mediated by phase transfer catalysts (PTCs) [11] were developed. More recently,s ynergistic catalysis [12] and CÀHb ond oxygenation [13] were also applied to the asymmetric construction of five-membered spirocyclico xindoles.…”