Organocatalytic Conjugate Addition of Nitroalkanes to 3-Ylidene Oxindoles: A Stereocontrolled Diversity Oriented Route to Oxindole Derivatives

Organocatalytic asymmetric Friedel–Crafts alkylation/hemiketalization/lactonization cascade reactions: highly enantioselective synthesis of furo[2,3-b]benzofuranones

A highly diastereo- and enantioselective organocatalytic Friedel–Crafts alkylation/hemiketalization/lactonization cascade reaction generating furo[2,3-b]benzofuranones in good to excellent yields with high stereoselectivities.

Catalytic Asymmetric Synthesis of Chiral Bis(indolyl)methanes Using a Ts-PyBidine-Nickel Complex

A chiral tosyl-substituted bis(imidazolidine)pyridine Ts-PyBidine-nickel complex was an efficient catalyst for Friedel-Crafts reaction of indoles with methylene indolinones to give bisindolylmethane compounds having differently oxidized indole units with high enantioselectivities. Alkylation of the products proceeded smoothly in a highly diastereoselective manner, providing an all-carbon quaternary carbon center without significant loss of enantiomeric excess.

Fused electron deficient semiconducting polymers for air stable electron transport

Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.

Semiconducting polymers are usually prepared by transition metal mediated coupling reactions that cause problems for sustainability and biological applications. Here the authors synthesise fused electron deficient polymers that are air stable and have high electron affinities, via metal free aldol polymerisation reactions.

Non-Covalent Organocatalyzed Domino Reactions Involving Oxindoles: Recent Advances

The ubiquitous presence of spirooxindole architectures with several functionalities and stereogenic centers in bioactive molecules has been appealing for the development of novel methodologies seeking their preparation in high yields and selectivities. Expansion and refinement in the field of asymmetric organocatalysis have made possible the development of straightforward strategies that address these two requisites. In this review, we illustrate the current state-of-the-art in the field of spirooxindole synthesis through the use of non-covalent organocatalysis. We aim to provide a concise overview of very recent methods that allow to the isolation of unique, densely and diversified spirocyclic oxindole derivatives with high structural diversity via the use of cascade, tandem and domino processes.

Catalyst-free synthesis of 3-alkenyloxindoles from isatin-derived Morita–Baylis–Hillman carbonates

A variety of biologically and synthetically useful 3-alkenyloxindoles were rapidly synthesised via an SN2′-type allylic substitution reaction of isatin-derived Morita–Baylis–Hillman carbonates with sodium sulfinates. The syntheses were conducted under catalyst-free reaction conditions and good to excellent product yields (up to 96%) and Z/E selectivities (up to >20:1) were obtained.

BF3·OEt2 Mediated Regioselective Reaction of Electron-Rich Arenes with 3-Ylidene Oxindoles

A BF₃·OEt₂ mediated novel and regioselective protocol for the construction of a C-C bond between 3-ylidene oxindoles and electron-rich arenes has been successfully accomplished. The reaction was compatible with a wide variety of electron-rich arenes. A cascade reaction of 3-ylidene oxindoles with phenols and β-naphthol resulted in 2,3-difunctionalized benzofuran and lactone bearing indoline-2-one scaffolds under same conditions.

Diastereo- and enantioselective phase-transfer alkylation of 3-substituted oxindoles with racemic secondary alkyl halides

A catalytic asymmetric alkylation of fully substituted enolates with racemic, non-activated secondary alkyl halides is described.

Scandium triflate-catalyzed selective ring opening and rearrangement reaction of spiro-epoxyoxindole and carbonyl compounds

Scandium triflate-catalyzed reactions between spiro-epoxyoxindole and carbonyl compounds have been disclosed. Furthermore, an unprecedented rearrangement takes place to yield alkylidene oxindoles when aromatic aldehydes are used as carbonyl components.

Construction of highly enantioselective spiro-oxindole derivatives with fused chromene via organocascade catalysis

A first highly enantioselective addition of naphthols and sesamol to indolylidene cyanoacetate derived from isatins was carried out in the presence of bi-functional quinine thiourea as organocatalyst.

Novel ferrocene-based bifunctional amine-thioureas for asymmetric Michael addition of acetylacetone to nitroolefins

An efficient method was developed to synthesize ferrocene-based bifunctional amine-thioureas bearing multiple hydrogen-bonding donors. Asymmetric Michael addition of acetylacetone to nitroolefins catalyzed by these novel bifunctional catalysts affords the Michael adducts in high yield and moderate to excellent enantioselectivities. Multiple hydrogen-bonds play an important role in accelerating the reaction.

Highly stereoselective [4+2] and [3+2] spiroannulations of 2-(2-oxoindolin-3-ylidene)acetic esters catalyzed by bifunctional thioureas

A new Michael-Michael cascade reaction between 2-(2-oxoindolin-3-ylidene)acetic esters 1 and nitroenoates 2, catalyzed by bifunctional thioureas, is investigated. The combination of the two Michael reactions results in a novel and facile [4+2] or [3+2] spiroannulation process, which is characterized by the following features: 1) two carbon-carbon bonds and four stereocenters, including a quaternary spiro carbon, are formed under mild conditions; 2) an unprecedented and stereochemically defined substitution pattern on the spirocarbocyclic unit is obtained; 3) the double-bond configuration of the donor-acceptor nitroenoate 2 determines the absolute configuration of the spiro center, whereas the remaining stereocenters are formed under control of the catalyst. The effect on the final stereochemical outcome of structural variations of each starting material, catalyst, and experimental conditions is analyzed in detail. In particular, the use of specifically designed chiral nitroenoates enables diverse polyfunctional spirocyclohexane derivatives containing six consecutive stereogenic centers to be constructed. To our knowledge, this is the first asymmetric organocatalytic strategy enabling both five- and six-membered β-nitro spirocarbocyclic oxindoles.

Asymmetric synthesis of poly-substituted spirocyclohexane oxindole via a squaramide catalyzed cascade Michael–Michael–aldol sequence

Asymmetric synthesis of spirocyclohexane oxindoles bearing six contiguous stereocenters has been achieved in good yields (up to 85%) with excellent stereoselectivities (>20 : 1 dr, >99% ee).

Asymmetric Michael addition reactions of nitroalkanes to 2-furanones catalyzed by bifunctional thiourea catalysts

The first bifunctional thiourea catalyzed asymmetric Michael addition reactions of nitroalkanes to 2-furanones are described.

Ferrocene as a scaffold for effective bifunctional amine–thiourea organocatalysts

This work demonstrates that ferrocene could be an excellent scaffold for chiral organocatalysts.