Quinidine Thiourea-Catalyzed Aldol Reaction of Unactivated Ketones: Highly Enantioselective Synthesis of 3-Alkyl-3-hydroxyindolin-2-ones

Catalytic Enantioselective Ynamide Additions to Isatins: Concise Access to Oxindole Alkaloids

The highly enantioselective addition of terminal ynamides to a variety of isatins, catalyzed by a bisoxazolidine copper complex under mild, base-free reaction conditions, is described. The reaction is broad in scope, scalable, applicable to unprotected isatins, and provides efficient access to 3-hydroxyoxindoles carrying a tetrasubstituted chiral center with excellent yields and enantioselectivities. Synthetically versatile, multifunctional 3-hydroxyindolinones are obtained by hydration, partial hydrogenation, or hydroxyacyloxylation of the ynamide moiety at room temperature and exhaustive hydrogenation followed by reductive detosylation and spontaneous cyclization affords cinchonamidine alkaloids.

Enantioselective synthesis of spiro[4H-pyran-3,3'-oxindole] derivatives catalyzed by cinchona alkaloid thioureas: Significant water effects on the enantioselectivity

An efficient stereoselective three-component reaction for the synthesis of functionalized spiro[4H-pyran-3,3'-oxindole] derivatives was realized through an organocatalyzed domino Knoevenagel/Michael/cyclization reaction using a cinchonidine-derived thiourea as the catalyst. Using water as the additive was found to improve the product ee values significantly. Under the optimized conditions, the reactions between isatins, malononitrile, and 1,3-dicarbonyl compounds yield the desired spirooxindole products in good yields (71-92%) and moderate to high ee values (up to 87% ee).

Autoxidation/Aldol Tandem Reaction of 2-Oxindoles with Ketones: A Green Approach for the Synthesis of 3-Hydroxy-2-Oxindoles

In the presence of tetrabutylammonium fluoride and molecular sieves (MS) 4 Å in DMF, an efficient autoxidation reaction of 2-oxindoles with ketones under air at room temperature has been developed. This approach may provide a green, practical, and metal-free protocol for a wide range of biologically important 3-hydroxy-3-(2-oxo-alkyl)-2-oxindoles.

Acetaldehyde: A Small Organic Molecule with Big Impact on Organocatalytic Reactions

Stereocontrolled formation of carbon-carbon and carbon-heteroatom bonds through asymmetric organocatalysis is a formidable challenge for modern synthetic chemistry. Among the most significant contributions to this field are the transformations involving the use of acetaldehyde or α-heteroatom-substituted acetaldehydes for constructing valuable synthons (e.g., amino acid derivatives and hydroxycarbonyl). In this Minireview, versatile (enantioselective) organocatalytic transformations are discussed.

Cross-Aldol Reaction of Isatin with Acetone Catalyzed by Leucinol: A Mechanistic Investigation

Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin (1 a) and acetone, catalyzed by L-leucinol (3 a), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn-enamine 6, catalyzed by isatin, was identified as the rate-determining step by both the calculations (ΔG(≠) =26.1 kcal mol(-1) for the analogous L-alaninol, 3 b) and the kinetic isotope effect (kH /kD =2.7 observed for the reaction using [D6 ]acetone). The subsequent reaction of the syn-enamine 6 with isatin produces (S)-2 a (calculated ΔG(≠) =11.6 kcal mol(-1) ). The calculations suggest that the overall stereochemistry is controlled by two key events: 1) the isatin-catalyzed formation of the syn-enamine 6, which is thermodynamically favored over its anti-rotamer 7 by 2.3 kcal mol(-1) ; and 2) the high preference of the syn-enamine 6 to produce (S)-2 a on reaction with isatin (1 a) rather than its enantiomer (ΔΔG(≠) =2.6 kcal mol(-1) ).

Asymmetric Aldol Reaction of 3-Acetyl-2H-chromen-2-ones and Isatins Catalyzed by a Bifunctional Quinidine Urea Catalyst

The asymmetric aldol reaction of 3-acetyl-2H-chromen-2-ones and isatins has been realized by using a bifunctional quinidine-derived urea as the catalyst. The corresponding 3-hydroxyoxindole derivatives containing a 2H-chromen-2-one moiety were obtained in good yields and high enantioselectivities. When (Z)-ethyl 2-benzylideneacetoacetate was used as the substrate, a mixture of two diastereomers (both Z and E) was obtained due to the isomerization of the double bond under the reaction conditions.