All-carbon quaternary stereogenic centers in acyclic systems through the creation of several C-C bonds per chemical step

Diastereo- and Enantioselective Synthesis of Spirooxindoles with Contiguous Tetrasubstituted Stereocenters via Catalytic Coupling of Two Tertiary Radicals

The oxidative N-heterocyclic carbene-catalyzed [3 + 2] annulation of β,β-disubstituted enals and dioxindoles was developed, giving the spirocyclic oxindole-γ-lactones bearing two contiguous tetrasubstituted stereocenters in good yields with excellent diastereoselectivities and good enantioselectivities.

Decarboxylation-promoted Pd-catalyzed asymmetric propargylic [3 + 2] annulation for the enantioselective construction of a quaternary stereocenter in 2,3-dihydrofurans

The enantioselective construction of a quaternary stereocenter in 2,3-dihydrofuran frameworks has been realized via the palladium-catalyzed asymmetric [3 + 2] cycloaddition of tertiary propargylic carbonates with β-ketoesters enabled by a chiral ferrocene/benzimidazole-based bidentate P,N-ligand. The reaction was significantly promoted by loss of CO₂ to irreversibly form π-propargylpalladium or allenylpalladium intermediates. This protocol features a good tolerance of functional groups in both tertiary propargylic carbonates and β-ketoesters, thereby delivering a variety of highly functionalized chiral 2,3-dihydrofurans bearing a quaternary stereocenter at the 2-position and an exocyclic double bond at the 3-position in good chemical yields and high enantioselectivities (up to 98% ee).

Catalytic asymmetric propargyl- and allylboration of hydrazonoesters: a metal-free approach to sterically encumbered chiral α-amino acid derivatives

Metal-free asymmetric catalysis for the synthesis of sterically encumbered amino-acids was developed using allyl- and allenylboronic acid reagents.

Electrophilic fluorination of stereodefined disubstituted silyl ketene hemiaminals en route to tertiary α-fluorinated carbonyl derivatives

A highly diastereoselective synthesis of tertiary α-fluoro carbonyl compounds is reported in only two chemical steps from a simple alkyne through the reaction of stereodefined fully substituted silyl ketene hemiaminal derivatives with Selectfluor.

Acyclic Quaternary Carbon Stereocenters via Enantioselective Transition Metal Catalysis

Whereas numerous asymmetric methods for formation of quaternary carbon stereocenters in cyclic systems have been documented, the construction of acyclic quaternary carbon stereocenters with control of absolute stereochemistry remains a formidable challenge. This Review summarizes enantioselective methods for the construction of acyclic quaternary carbon stereocenters from achiral or chiral racemic reactants via transition metal catalysis.

Stereoselective Tandem Bis-Electrophile Couplings of Diborylmethane

A copper-catalyzed three-component linchpin coupling method for the stereoselective union of readily available epoxides and allyl electrophiles is disclosed. Transformations employ [B(pin)]₂-methane as a conjunctive reagent, resulting in the formation of two C-C bonds at a single carbon center bearing a C(sp³) organoboron functional group. Products are obtained in 42-99% yield, and up to >20:1 dr. The utility of the approach is highlighted by stereospecific transformations entailing allylation, tandem cross coupling, and application to the synthesis 1,3-polyol motifs.

Asymmetric Synthesis of Chiral Cyclopentanes Bearing an All-Carbon Quaternary Stereocenter by Zirconium-Catalyzed Double Carboalumination

Herein, we report a zirconium-catalyzed enantio- and diastereoselective inter/intramolecular double carboalumination of unactivated 2-substituted 1,5-dienes, which provides efficient and direct access to chiral cyclopentanes through the generation of two stereocenters, including one all-carbon quaternary stereocenter, generally with excellent diastereo- and high enantioselectivity. This tandem carboalumination process creates two new C-C bonds as well as one C-Al bond, which can be oxidized in situ with O₂ or hydrolyzed. Furthermore, the obtained chiral cyclopentanes can be readily functionalized to provide various chiral compounds.

Efficient Access to All-Carbon Quaternary and Tertiary α-Functionalized Homoallyl-type Aldehydes from Ketones

β,γ-Unsaturated aldehydes with all-carbon quaternary or tertiary α-centers were rapidly assembled from ketones through a unique synthetic operation consisting of 1) C₁ homologation, 2) Lewis acid mediated epoxide-aldehyde isomerization, and 3) electrophilic trapping. The synthetic equivalence of a vinyl oxirane and a β,γ-unsaturated aldehyde is the key concept of this previously undisclosed tactic. Mechanistic studies and labeling experiments suggest that an aldehyde enolate is a crucial intermediate. The homologating carbenoid formation plays a critical role in determining the chemoselectivity.

Enantioselective Construction of Acyclic Quaternary Carbon Stereocenters: Palladium-Catalyzed Decarboxylative Allylic Alkylation of Fully Substituted Amide Enolates

We report a divergent and modular protocol for the preparation of acyclic molecular frameworks containing newly created quaternary carbon stereocenters. Central to this approach is a sequence composed of a (1) regioselective and -retentive preparation of allyloxycarbonyl-trapped fully substituted stereodefined amide enolates and of a (2) enantioselective palladium-catalyzed decarboxylative allylic alkylation reaction using a novel bisphosphine ligand.

Enantioselective Formation of CF3-Bearing All-Carbon Quaternary Stereocenters via C-H Functionalization of Methanol: Iridium Catalyzed Allene Hydrohydroxymethylation

Using an iridium catalyst modified by PhanePhos, CF3-allenes react with methanol to form branched products of hydrohydroxymethylation as single regioisomers with excellent levels of enantiomeric enrichment. This hydrogen autotransfer process enables catalytic enantioselective formation of acyclic CF3-bearing all-carbon quaternary stereocenters in the absence of stoichiometric metals or byproducts.

Mizoroki-Heck Cyclizations of Amide Derivatives for the Introduction of Quaternary Centers

We report non-decarbonylative Mizoroki-Heck reactions of amide derivatives. The transformation relies on the use of nickel catalysis and proceeds using sterically hindered tri- and tetrasubstituted olefins to give products containing quaternary centers. The resulting polycyclic or spirocyclic products can be obtained in good yields. Moreover, a diastereoselective variant of this method gives access to an adduct bearing vicinal, highly substituted sp3 stereocenters. These results demonstrate that amide derivatives can be used as building blocks for the assembly of complex scaffolds.

A unique Pd-catalysed Heck arylation as a remote trigger for cyclopropane selective ring-opening

Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C-C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres.

Stereodivergent Coupling of Aldehydes and Alkynes via Synergistic Catalysis Using Rh and Jacobsen's Amine

We report an enantioselective coupling between α-branched aldehydes and alkynes to generate vicinal quaternary and tertiary carbon stereocenters. The choice of Rh and organocatalyst combination allows for access to all possible stereoisomers with high enantio-, diastereo-, and regioselectivity. Our study highlights the power of catalysis to activate two common functional groups and provide access to divergent stereoisomers and constitutional structures.

Synthesis of spiro-oxoindoles through Pd-catalyzed remote C–H alkylation using α-diazocarbonyl compounds

In this communication we describe a new route to spiro-oxoindole derivatives through a novel Pd-catalyzed cascade process.

Selective construction of quaternary stereocentres in radical cyclisation cascades triggered by electron-transfer reduction of amide-type carbonyls

Radical cyclisation cascades triggered by electron-transfer to amide-type carbonyls using SmI₂–H₂O–LiBr, result in the selective construction of quaternary carbon stereocentres.

Zirconocene-assisted remote cleavage of C-C and C-O bonds: application to acyclic stereodefined metalated hydrocarbons

The molding of molecules through remote functionalisation has increasingly become popular as it provides original and flexible synthetic alternatives to classical retrosynthetic analysis. In this Perspective article, we summarise more than a decade of studies in the specific field of remote activation of inert C-C and C-O bonds using the unique abilities of organozirconocene species mainly from our own research group. By demonstrating that these reactions represent novel and powerful entries towards acyclic stereodefined reactive organometallic species, we aim to show the vast opportunities this concept-driven methodology discovery offers.

Enantioselective Formation of All-Carbon Quaternary Centers via C-H Functionalization of Methanol: Iridium-Catalyzed Diene Hydrohydroxymethylation

The first catalytic enantioselective C-C couplings of methanol (>30 × 106 tons/year) are reported. Insertion of 2-substituted dienes into the methanol C-H bond occurs in a regioselective manner to form all-carbon quaternary centers with excellent levels of enantioselectivity using an iridium-PhanePhos catalyst. Mechanistic studies corroborate a Curtin-Hammett scenario in which methanol dehydrogenation triggers rapid, reversible diene hydrometalation en route to regioisomeric allyliridium-formaldehyde pairs, yet single constitutional isomers are formed.

Enantioselective construction of branched 1,3-dienyl substituted quaternary carbon stereocenters by asymmetric allenyl Claisen rearrangement

The availability of enantiomerically enriched 1,3-dienyl substituted quaternary stereocenters is highly valuable for the synthesis of complex natural compounds. Despite great advances in the area of construction of alkenyl-substituted types, a general, practical catalytic system that works for enantioselective formation of 1,3-diene derivatives still remains to be developed. Herein, we disclose the first asymmetric Claisen rearrangement of allenyl vinyl ethers to access optically active β-ketoesters, containing branched 1,3-butadienyl substituted stereocenters. A variety of substrates bearing a range of useful functional groups were well tolerated, thus affording the corresponding products with excellent enantioselectivities (up to 99% ee) and high yields (up to 91%).

Enantioselective Generation of Adjacent Stereocenters in a Copper-Catalyzed Three-Component Coupling of Imines, Allenes, and Diboranes

A highly enantio- and diastereoselective copper-catalyzed three-component coupling affords the first general synthesis of homoallylic amines bearing adjacent stereocenters from achiral starting materials. The method utilizes a commercially available NHC ligand and copper source, operates at ambient temperature, couples readily available simple imines, allenes, and diboranes, and yields high-value homoallylic amines that exhibit versatile amino, alkenyl, and boryl units.

Enantioselective allylic alkylation of stereodefined polysubstituted copper enolates as an entry to acyclic quaternary carbon stereocentres

A sequence of regio- and stereoselective carbometalation followed by oxidation of ynamides leads to stereodefined fully substituted enolates that subsequently react with various functionalized allyl bromide reagents to provide the enantiomerically pure quaternary carbon stereocentre in the α-position to the carbonyl group.

A sequence of regio- and stereoselective carbometalation followed by oxidation of ynamides leads to stereodefined fully substituted enolates that subsequently react with various functionalized allyl bromide reagents to provide the expected products possessing an enantiomerically pure quaternary carbon stereocentre in the α-position to the carbonyl group in excellent yields and enantiomeric ratios after cleavage of the oxazolidinone moiety. Three new bonds are formed in a single-pot operation.

Acyclic quaternary centers from asymmetric conjugate addition of alkylzirconium reagents to linear trisubstituted enones

Synthetic methods for the selective formation of all carbon quaternary centres in non-cyclic systems are rare. Here we report highly enantioselective Cu-catalytic asymmetric conjugate addition of alkylzirconium species to twelve different acyclic trisubstituted enones.

Synthetic methods for the selective formation of all carbon quaternary centres in non-cyclic systems are rare. Here we report highly enantioselective Cu-catalytic asymmetric conjugate addition of alkylzirconium species to twelve different acyclic trisubstituted enones. A variety of sp³-hybridized nucleophiles generated by in situ hydrozirconation of alkenes with the Schwartz reagent can be introduced, giving linear products bearing quaternary centres with up to 98% ee. The method is tolerant of several important functional groups and 27 total examples are reported. The method uses a new chiral nonracemic phosphoramidite ligand in a complex with copper triflate as the catalyst. This work allows the straightforward stereocontrolled formation of a valuable structural motif using only a catalytic amount of chiral reagent.

Diastereodivergent combined carbometalation/zinc homologation/C-C fragmentation reaction as an efficient tool to prepare acyclic allylic quaternary carbon stereocenters

A new strategy has been developed to construct enantiomerically enriched acyclic allylic quaternary carbon stereocenters in a single-pot operation through a combined carbometalation/zinc homologation/fragmentation sequence. Proper tuning of the reaction conditions enables the synthesis of the two enantiomers starting from a single enantiomer of the starting material.

Enantioselective Organocatalyzed Transformations of β-Ketoesters

The β-ketoester structural motif continues to intrigue chemists with its electrophilic and nucleophilic sites. Proven to be a valuable tool within organic synthesis, natural product, and medicinal chemistry, reports on chiral β-ketoester molecular skeletons display a steady increase. With the reignition of organocatalysis in the past decade, asymmetric methods available for the synthesis of this structural unit has significantly expanded, making it one of the most exploited substrates for organocatalytic transformations. This review provides comprehensive information on the plethora of organocatalysts used in stereoselective organocatalyzed construction of β-ketoester-containing compounds.

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.

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.

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.