Organocatalytic Michael/Michael Cycloaddition Enabled Asymmetric Construction of Hexahydroxanthones with Skeletal Diversity

Enantioselective synthesis of isoxazole-containing spirooxindole tetrahydroquinolines via squaramide-catalysed cascade reactions

A class of o-sulfonylaminostyryl isoxazole synthons were designed and demonstrated to be useful building blocks in asymmetric cascade aza-Michael/Michael reaction with 3-olefinic oxindoles. This squaramide-catalysed cascade reaction afforded structurally complex isoxazole-containing spirooxindole tetrahydroquinolines bearing three contiguous stereocenters in good to excellent yields (up to 99%) with high diastereoselectivities (up to >20 : 1 dr) and enantioselectivities (up to 88% ee). Moreover, the gram-scale synthesis and synthetic transformations were also demonstrated.

Catalytic asymmetric Michael/cyclization reaction of 3-isothiocyanato thiobutyrolactone: an approach to the construction of a library of bispiro[pyrazolone-thiobutyrolactone] skeletons

Here, we demonstrate the first example of 3-isothiocyanato thiobutyrolactone serving as a useful building block in the Michael/cyclization reaction with alkylidene pyrazolones for the enantioselective construction of optically active structural bispiro[pyrazolone-thiobutyrolactone] skeletons containing three contiguous stereocenters with two spiroquaternary stereocenters. These products were smoothly afforded in up to 90% yield, >20 : 1 dr and >99% ee with chiral squaramide as the catalyst under mild conditions. Notably, this is also the first example of the merger of a spirocyclic pyrazolone scaffold with a spirocyclic thiobutyrolactone scaffold, potentially useful in medicinal chemistry.

Asymmetric Phase Transfer Catalysed Michael Addition of γ-Butenolide and N-Boc-Pyrrolidone to 4-Nitro-5-styrylisoxazoles

Herein we report the addition of acidic γ-butenolide and N-Boc-pyrrolidone to 4-nitro-5-styrylisoxazoles, a popular class of cinnamic ester synthetic equivalent. The reactions proceeded under the catalysis of Cinchona-based phase-transfer catalysts. Functionalised γ-butenolides were obtained in good isolated yields and moderate enantioselectivity (up to 74% ee).

Asymmetric synthesis of isoxazole and trifluoromethyl-containing 3,2'-pyrrolidinyl dispirooxindoles via squaramide-catalysed [3 + 2] cycloaddition reactions

A highly efficient squaramide-catalysed asymmetric domino Michael/Mannich [3 + 2] cycloaddition of 3-methyl-4-nitro-5-isatylidenyl-isoxazoles and N-2,2,2-trifluoroethylisatin ketimines was developed. A new class of complex and diverse-skeleton isoxazole and trifluoromethyl-containing 3,2'-pyrrolidinyl dispirooxindoles bearing four contiguous stereogenic centers including two adjacent spiro quaternary stereocentres were obtained in good to excellent yields (up to 99%) with excellent diastereoselectivities (>20 : 1 dr, in all cases) and enantioselectivities (up to 96% ee). Moreover, the potential utilities of the protocol have been demonstrated by gram-scale synthesis and further transformation experiments.

Diastereoselective construction of a library of structural bispiro[butyrolactone/valerolactone-pyrrolidine-indanedione] hybrids via 1,3-dipolar cycloaddition reactions

Herein, a highly efficient strategy that allows the diversity synthesis of a library of structural bispiro[butyrolactone-pyrrolidine-indanedione] hybrids is achieved effectively by means of 1,3-dipolar cycloadditions of α,β-unsaturated butyrolactones/valerolactones as dipolarophiles...

3-Vinyl oxindole-chromone synthon as a skeletal reconstruction reactant for the synthesis of 2-hydroxy benzoyl pyridones

The first example of 3-vinyl oxindole-chromones in the ring opening and recyclization reaction.

Synthesis of 3,3-Dihalogenated 2-Aminochromanones via Tandem Dihalogenation and Cyclization of o-Hydroxyarylenaminones with NXS (X = Cl or Br)

An unprecedented method for the synthesis of dichlorinated and dibrominated 2-amino-substituted chromanones is developed by employing enaminones and NCS/NBS as starting materials under microwave irradiation. The reactions proceed quickly to deliver products without using any catalyst or additive, thus providing practical access to 3,3-dihalogenated 2-aminochromanones.

Asymmetric construction of six vicinal stereogenic centers on hexahydroxanthones via organocatalytic one-pot reactions

Inspired by the chemistry and biology of hexahydroxanthones, herein we report an organocatalytic Michael-Michael-Aldol-decarboxylation reaction that provides efficient access to biologically interesting fully substituted hexahydroxanthones bearing six contiguous stereogenic centers from readily accessible materials in acceptable yields (up to 63%) and excellent stereoselectivities (up to 10 : 1 dr and >99% ee). In other words, the reaction efficiently produces three chemical bonds and up to six vicinal stereogenic centers in a one-pot operation. In particular, to our knowledge, this is an asymmetric organocatalytic strategy enabling the first construction of six vicinal stereogenic centers on non-spirocyclic hexahydroxanthone frameworks.

Synthesis of methanesulfone-containing tetrasubstituted carbon stereocenters

A methanesulfonylation reaction for the synthesis of sulfone-containing tetrasubstituted carbon stereocenters is described for the first time by simple treatment of indanedione-chromanone synthons with Et3N and easily accessible MsCl without any use of organometallic chemistry. This technology gave the corresponding valuable chromone-based 2-methanesulfonylated 1,3-indanediones in good yields (up to 89% yield) under mild conditions. The present work provides an attractive strategy for the construction of biologically interesting sulfone-containing tetrasubstituted carbon stereocenters, which might be valuable in medicinal chemistry.

Chromone–indanedione reactant: a bifunctional 3C synthon for diastereoselective construction of skeleton-diversified bispiro-[chromanocyclopentane-oxindole-indanedione]

A new type of bifunctional 3C synthon, a chromone–indanedione precursor, was employed for diastereoselective Michael/Michael cycloaddition with methyleneindolinones to generate a series of potentially bioactive bispiro-[chromanocyclopentane-oxindole-indanedione] frameworks with skeletal diversity in a single operation.

Recent advances of chromone-based reactants in the catalytic asymmetric domino annulation reaction

Chiral polycyclic chromanones are important heterocyclic frameworks that constitute the core structures of many natural products and bioactive molecules.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Transition-metal-free cascade benzannulations for synthesizing 2-hydroxybenzophenones

A set of cascade benzannulations of readily accessible chromone-3-carboxaldehydes and γ-nitroaldehydes for synthesizing biologically relevant 2-hydroxybenzophenones has been developed. The cascade was found to provide a transition-metal-free strategy for synthesizing 2-hydroxybenzophenones in acceptable yields (up to 57%).

Coumarin-3-formylpyrazoles as 3-carbon synthons in cyclocondensation for the synthesis of spiro-fused pentacyclic spirooxindoles

Coumarin-3-formylpyrazoles have been synthesized and applied as 3-carbon synthons in reaction with 3-hydroxyoxindoles by using DABCO as the catalyst. A range of structurally diverse spiro-fused pentacyclic spirooxindoles, bearing a spirooxindole-γ-lactone and a 3,4-dihydrocoumarin substructure, could be smoothly obtained in good to excellent yields (up to 99%) with excellent diastereoselectivities (all cases >20 : 1 dr). The asymmetric version of this tandem reaction was preliminarily investigated by using chiral organocatalysts.

Enantioselective dearomative [3 + 2] annulation of 3-hydroxy chromanones with azonaphthalenes

Enantioselective dearomative [3 + 2] annulation of 3-hydroxy chromanones with azonaphthalenes provided a large variety of chromanone fused indolines in moderate to good yields with generally good enantioselectivities.

An organocatalytic domino Michael addition strategy: construction of bispiro[oxindole-thiazolidinone-hexahydroxanthone]s with five contiguous stereocenters

An efficient squaramide-catalyzed domino Michael addition for the stereoselective synthesis of bispiro[oxindole-thiazolidinone-hexahydroxanthone]s in good to excellent yields with excellent stereoselectivities was developed.

Thermal-mediated [1,3]-hydrogen transfer as the key step: access to oxindole-chromone hybrid collection with structural diversity

Inspired by the chemistry and biology of chromone and oxindole derivatives, herein we report the first example of thermal-mediated [1,3]-hydrogen transfer as the key step for the efficient synthesis of oxindole-chromone hybrid collections 2, which avoids additional catalyst and solvent conditions. All the oxindole-chromones 2 are smoothly obtained in >99% yields in all cases, avoiding column chromatography purification. In particular, the products 2 can act as potential synthons for further elaboration in structural diversity, which might be valuable in organic and medicinal chemistry.

An unexpected cascade reaction of 3-hydroxyoxindoles with coumarin-3-carboxylates to construct 2,3-dihydrobenzofuran spirooxindoles

An unexpected Michael addition-inspired ring-opening/closure cascade reaction of 3-hydroxyoxindoles with coumarin-3-carboxylates was developed.

Stereocontrolled construction of six vicinal stereogenic centers on a hexahydroxanthone framework through a formal [2+1+3] annulation

The first example of a bifunctional donor–donor 3C synthon formed in situ from an activated methine with nitromethane through a [2+1] Michael addition, further directing a one-pot organocascade Michael/Henry cycloaddition was developed.

An asymmetric iminium ion catalysis-enabled cascade cycloaddition reaction of chromone-oxindole synthons with enals: construction of a spirooxindole–hexahydroxanthone framework

We report the first asymmetric iminium ion catalysis-enabled cascade cycloaddition reaction of bifunctional chromone-oxindole synthons and α,β-unsaturated aldehydes.