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.

Stereoselective synthesis of C3-tetrasubstituted oxindoles via copper catalyzed asymmetric propargylation

Herein, a copper catalyzed asymmetric propargylation of 2-oxindole-3-carboxylate esters with terminal propargylic esters is described. This strategy successfully provides a direct approach to constructing a broad range of chiral C3-tetrasubstituted oxindoles with contiguous tertiary and quaternary carbon stereocenters in high yields and excellent enantioselectivities (16 examples, up to 99% yield and 98% ee). Moreover, the diastereoisomers of the two newly formed stereocenters can be separated by silica gel chromatography, thereby providing a valuable stereoselective access to all four possible stereoisomers of C3-tetrasubstituted oxindoles.

Asymmetric addition of α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid

Asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid catalyst, generates an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity.

We describe the asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid, generating an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity. The products are easily transformed into their corresponding 1,5- and 1,4-ketoaldehyde derivatives, which are both important building blocks in organic synthesis.

3-Pyrrolyl-oxindoles as efficient nucleophiles for organocatalytic asymmetric synthesis of structurally diverse 3,3′-disubstituted oxindole derivatives

An organocatalytic asymmetric reaction of 3-pyrrolyl-oxindoles to nitroalkenes was developed to afford a range of 3-pyrrolyl-3,3′-disubstituted oxindoles in excellent yields.

An asymmetric allylic alkylation reaction of 3-alkylidene oxindoles

An efficient asymmetric allylic alkylation reaction with respect to 3-alkylidene oxindoles and racemic MBH carbonate has been achieved.

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 synthesis of γ-tetrasubstituted nitrosulfonyl carboxylates and amides vial-tert-leucine-derived-squaramide catalyzed conjugate addition of nitrosulfones to acrylates and acrylamides

A t-leucine-derived squaramide catalyzed reaction of α-nitrosulfones with acrylates/acrylamides provides γ-tetrasubstituted γ-nitro-γ-sulfonyl carboxylates/amides in excellent yield and enantioselectivity.

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.

Electrophilicities of bissulfonyl ethylenes

Kinetics of the reactions of bissulfonyl ethylenes with various carbanions, a sulfur ylide, and siloxyalkenes have been investigated photometrically at 20 °C. The second-order rate constants have been combined with the known nucleophile- specific parameters N and s(N) for the nucleophiles to calculate the empirical electrophilicity parameters E of bissulfonyl ethylenes according to the linear free energy relationship log k(20 °C)=s(N)(N+E). Structure-reactivity relationships are discussed, and it is shown that the electrophilicity parameters E derived in this work can be employed to define the synthetic potential of bissulfonyl ethylenes as Michael acceptors.