Catalytic enantioselective synthesis of quaternary carbon stereocentres

Modular, Catalytic Enantioselective Construction of Quaternary Carbon Stereocenters by Sequential Cross-Coupling Reactions

The catalytic Suzuki-Miyaura cross-coupling with chiral γ,γ-disubstituted allylboronates in the presence of RuPhos ligand occurs with high regioselectivity and enantiospecificity, furnishing nonracemic compounds with quaternary centers. Mechanistic experiments suggest that the reaction occurs by transmetalation with allyl migration, followed by rapid reductive elimination.

Pd-Catalyzed C(sp(3))-H Functionalization/Carbenoid Insertion: All-Carbon Quaternary Centers via Multiple C-C Bond Formation

A Pd-catalyzed C(sp(3))-H functionalization/carbenoid insertion is described. The method allows for the rapid synthesis of bicyclic frameworks, generating all-carbon quaternary centers via multiple C-C bond formations in a straightforward manner.

Asymmetric [3 + 2] Cycloaddition of Vinylcyclopropanes and α,β-Unsaturated Aldehydes by Synergistic Palladium and Organocatalysis

The stereoselective [3 + 2] cycloaddition between vinylcyclopropanes and α,β-unsaturated aldehydes promoted by combined palladium and organocatalysis is disclosed. The unique synergistic catalytic system allows for the stereoselective formation of highly substituted cyclopentanes with up to four stereocenters in high yields and selectivities. Vinylcyclopropanes with two different geminal substituents facilitate the formation of cyclopentanes containing a quaternary stereocenter. Furthermore, the developed reaction performs well on gram scale, and a number of transformations are demonstrated.

Asymmetric Catalysis with CO2 : The Direct α-Allylation of Ketones

Quaternary stereocenters are found in numerous bioactive molecules. The Tsuji-Trost reaction has proven to be a powerful C-C bond forming process, and, at least in principle, should be well suited to access quaternary stereocenters via the α-allylation of ketones. However, while indirect approaches are known, the direct, catalytic asymmetric α-allylation of branched ketones has been elusive until today. By combining "enol catalysis" with the use of CO2 as a formal catalyst for asymmetric catalysis, we have now developed a solution to this problem: we report a direct, highly enantioselective and highly atom-economic Tsuji-Trost allylation of branched ketones with allylic alcohol. Our reaction delivers products bearing quaternary stereocenters with high enantioselectivity and water as the sole by-product. We expect our methodology to be of utility in asymmetric catalysis and inspire the design of other highly atom-economic transformations.

Iridium-Catalyzed Diastereoselective and Enantioselective Allylic Substitutions with Acyclic α-Alkoxy Ketones

The asymmetric alkylation of acyclic ketones is a longstanding challenge in organic synthesis. Reported herein are diastereoselective and enantioselective allylic substitutions with acyclic α-alkoxy ketones catalyzed by a metallacyclic iridium complex to form products with contiguous stereogenic centers derived from the nucleophile and electrophile. These reactions occur between allyl methyl carbonates and unstabilized copper(I) enolates generated in situ from acyclic α-alkoxy ketones. The resulting products can be readily converted into enantioenriched tertiary alcohols and tetrahydrofuran derivatives without erosion of enantiomeric purity.

Stereoselective Formation of Fully Substituted Ketone Enolates

The application of stereochemically defined acyclic fully substituted enolates of ketones to the enantioselective synthesis of quaternary carbon stereocenters would be highly valuable. Herein, we describe an approach leading to the formation of several new stereogenic centers through a combined metalation-addition of a carbonyl-carbamoyl transfer to reveal in situ stereodefined α,α-disubstituted enolates of ketone as a single stereoisomer. This approach could produce a series of aldol and Mannich products from enol carbamate with excellent diastereomeric ratios.

Synthetic Strategies toward Natural Products Containing Contiguous Stereogenic Quaternary Carbon Atoms

Strategies for the total synthesis of complex natural products that contain two or more contiguous stereogenic quaternary carbon atoms in their intricate structures are reviewed with 12 representative examples. Emphasis has been put on methods to create quaternary carbon stereocenters, including syntheses of the same natural product by different groups, thereby showcasing the diversity of thought and individual creativity. A compendium of selected natural products containing two or more contiguous stereogenic quaternary carbon atoms and key reactions in their total or partial syntheses is provided in the Supporting Information.

Rhodium-Catalyzed Enantioselective Cycloisomerization to Cyclohexenes Bearing Quaternary Carbon Centers

We report a Rh-catalyzed enantioselective cycloisomerization of α,ω-heptadienes to afford cyclohexenes bearing quaternary carbon centers. Rhodium(I) and a new SDP ligand promote chemoselective formation of a cyclohex-3-enecarbaldehyde motif that is inaccessible by the Diels-Alder cycloaddition. Various α,α-bisallylaldehydes rearrange to generate six-membered rings by a mechanism triggered by aldehyde C-H bond activation. Mechanistic studies suggest a pathway involving regioselective carbometalation and endocyclic β-hydride elimination.

Construction of Quaternary Stereogenic Carbon Centers through Copper-Catalyzed Enantioselective Allylic Alkylation of Azoles

Copper-catalyzed enantioselective allylic alkylation of azoles with γ,γ-disubstituted primary allylic phosphates was achieved using a new chiral N-heterocyclic carbene ligand bearing a naphtholic hydroxy group. This reaction occurred with excellent branch regioselectivity and high enantioselectivity, thus forming a controlled all-carbon quaternary stereogenic center at the position α to the heteroaromatic ring.

Direct Catalytic Asymmetric Mannich Reactions for the Construction of Quaternary Carbon Stereocenters

Herein, we report a Zn-ProPhenol catalyzed Mannich reaction using α-branched ketones as nucleophilic partners for the direct enantio- and diastereoselective construction of quaternary carbon stereocenters. The reaction can be run on a gram-scale with a low catalyst loading without impacting its efficiency. Moreover, the Mannich adducts can be further elaborated with complete diastereocontrol to access molecules possessing complex stereotriads.

Asymmetric copper-catalyzed C-N cross-couplings induced by visible light

Despite a well-developed and growing body of work in copper catalysis, the potential of copper to serve as a photocatalyst remains underexplored. Here we describe a photoinduced copper-catalyzed method for coupling readily available racemic tertiary alkyl chloride electrophiles with amines to generate fully substituted stereocenters with high enantioselectivity. The reaction proceeds at -40°C under excitation by a blue light-emitting diode and benefits from the use of a single, Earth-abundant transition metal acting as both the photocatalyst and the source of asymmetric induction. An enantioconvergent mechanism transforms the racemic starting material into a single product enantiomer.

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.

Gold-catalyzed construction of two adjacent quaternary stereocenters via sequential C–H functionalization and aldol annulation

A novel gold-catalyzed intermolecular C–H functionalization and aldol cyclization for the construction of two adjacent quaternary centers is presented.

Asymmetric dual catalysis via fragmentation of a single rhodium precursor complex

A strategy for dual transition metal catalysis and organocatalysis is reported via disintegration of a single rhodium complex. Conveniently, the chiral-at-metal rhodium precatalyst can be synthesized in just two steps starting from rhodium trichloride without the need for any chromatography.

Facile synthesis of enantioenriched phenol-sulfoxides and their aluminum complexes

Chiral phenolic p-tolylsulfoxides, t-butylsulfoxides and well-defined aluminum complexes were prepared by short synthetic routes from readily available starting materials.

Enantioselective syntheses of indanes: from organocatalysis to C–H functionalization

The indanyl core is ubiquitous in a large variety of drugs and natural products. Remarkable recent progress has been accomplished in the step-economical assembly of functionalization of chiral indanes by means of enantioselective catalysis, with major progress being achieved in organocatalysis and C–H activation chemistry.

Sequential Au(i)/chiral tertiary amine catalysis: a tandem C–H functionalization of anisoles or a thiophene/asymmetric Michael addition sequence to quaternary oxindoles

We report an unprecedented sequential Au(i)/bifunctional tertiary amine catalysis, which enables a tandem C–H functionalization of weak nucleophiles (anisoles or thiophenes) and asymmetric Michael addition for the highly enantioselective synthesis of quaternary oxindoles.

The catalytic enantioselective synthesis of tetrahydroquinolines containing all-carbon quaternary stereocenters via the formation of aza-ortho-xylylene with 1,2-dihydroquinoline as a precursor

Tetrahydroquinolines (THQs) with an all-carbon quaternary stereocenter were effectively obtained via the in situ formation of aza-ortho-xylylene (AOX) with easily accessible 1,2-dihydroquinolines as precursors.

Organocatalytic 1,4-Addition Reaction of 2-Formyl(thio)esters to Vinylketones: An Efficient Access to Acyclic Chiral Building Blocks with a Quaternary Carbon Stereocenter

2-Formyl(thio)esters were utilized as pronucleophiles to obtain less-accessible acyclic chiral building blocks bearing versatile functional groups on a quaternary carbon atom for enantioselective 1,4-addition to vinylketones. To achieve high enantioselectivity in the present 1,4-addition reaction, thiourea-tertiary amines containing a bulky chiral backbone were developed as catalysts, and several derivatizations of the products were performed to demonstrate the synthetic utility of the products.

Enantioselective Dehydrogenative Heck Arylations of Trisubstituted Alkenes with Indoles to Construct Quaternary Stereocenters

An enantioselective, intermolecular dehydrogenative Heck arylation of trisubstituted alkenes to construct remote quaternary stereocenters has been developed. Using a new chiral pyridine oxazoline ligand, good to high enantioselectivity is achieved for various combinations of indole derivatives and trisubstituted alkenes. However, some combinations of substrates led to lower enantioselectivity, which provided the impetus to use structure enantioselectivity correlations to design a better performing ligand.

Nonenzymatic enantioselective synthesis of all-carbon quaternary centers through desymmetrization

The asymmetric desymmetrization of meso or prochiral compounds containing an all-carbon quaternary center is an attractive alternative to classical synthetic approaches aimed at the asymmetric formation of a new C-C bond. This review focuses on nonenzymatic desymmetrizations that utilize transition metal catalysts or organocatalysts to distinguish between enantiotopic groups to generate enantioenriched compounds containing all-carbon quaternary stereocenters.

Concise Enantioselective Synthesis of Oxygenated Steroids via Sequential Copper(II)-Catalyzed Michael Addition/Intramolecular Aldol Cyclization Reactions

A new scalable enantioselective approach to functionalized oxygenated steroids is described. This strategy is based on chiral bis(oxazoline) copper(II) complex-catalyzed enantioselective and diastereoselective Michael reactions of cyclic ketoesters and enones to install vicinal quaternary and tertiary stereocenters. In addition, the utility of copper(II) salts as highly active catalysts for the Michael reactions of traditionally unreactive β,β'-enones and substituted β,β'-ketoesters that results in unprecedented Michael adducts containing vicinal all-carbon quaternary centers is also demonstrated. The Michael adducts subsequently undergo base-promoted diastereoselective aldol cascade reactions resulting in the natural or unnatural steroid skeletons. The experimental and computational studies suggest that the torsional strain effects arising from the presence of the Δ(5)-unsaturation are key controlling elements for the formation of the natural cardenolide scaffold. The described method enables expedient generation of polycyclic molecules including modified steroidal scaffolds as well as challenging-to-synthesize Hajos-Parrish and Wieland-Miescher ketones.