Asymmetric construction of quaternary stereocenters by direct conjugate addition of oxindoles to enone

Asymmetric Synthesis of Arboduridine

The first asymmetric total synthesis of the monoterpenoid indole alkaloid arboduridine has been accomplished. The tricyclic A/B/D ring system was constructed by an enantioselective Michael reaction followed by intramolecular nucleophilic addition. Intramolecular α-amination of a ketone forged the piperidine ring, while a Horner-Wadsworth-Emmons (HWE) reaction was used to form the pyrrolidine ring. A reduction cyclization cascade led to formation of the tetrahydrofuran ring.

Organocatalytic asymmetric Michael addition of 3-substituted oxindoles to α,β-unsaturated acyl phosphonates for the synthesis of 3,3′-disubstituted oxindoles with chiral squaramides

The first Michael addition of 3-monosubstituted oxindoles to α,β-unsaturated acyl phosphonates is investigated to give 3,3′-disubstituted oxindoles with excellent results.

Enantioselective Michael addition of 3-aryl-substituted oxindoles to methyl vinyl ketone catalyzed by a binaphthyl-modified bifunctional organocatalyst

The enantioselective conjugate addition reaction of 3-aryl-substituted oxindoles with methyl vinyl ketone promoted by binaphthyl-modified bifunctional organocatalysts was investigated. The corresponding Michael adducts, containing a quaternary center at the C3-position of the oxindoles, were generally obtained in high yields with excellent enantioselectivities (up to 91% ee).

Organocatalytic asymmetric conjugate addition of 3-monosubstituted oxindoles to (E)-1,4-diaryl-2-buten-1,4-diones: a strategy for the indirect enantioselective furanylation and pyrrolylation of 3-alkyloxindoles

An asymmetric conjugate addition of 3-monosubstituted oxindoles to a range of (E)-1,4-diaryl-2-buten-1,4-diones, catalyzed by commercially available cinchonine, is described. This organocatalytic asymmetric reaction affords a broad range of 3,3'-disubstituted oxindoles that contain a 1,4-dicarbonyl moiety and vicinal quaternary and tertiary stereogenic centers in high-to-excellent yields (up to 98%), with excellent diastereomeric and moderate-to-high enantiomeric ratios (up to 99:1 and 95:5, respectively). Subsequently, cyclization of the 1,4-dicarbonyl moiety in the resultant Michael adducts under different Paal-Knorr conditions results in two new kinds of 3,3'-disubstituted oxindoles--3-furanyl- and 3-pyrrolyl-3-alkyl-oxindoles--in high yields and good enantioselectivities. Notably, the studies presented here sufficiently confirm that this two-step strategy of sequential conjugate addition/Paal-Knorr cyclization is not only an attractive method for the indirect enantioselective heteroarylation of 3-alkyloxindoles, but also opens up new avenues toward asymmetric synthesis of structurally diverse 3,3'-disubstituted oxindole derivatives.