Rhodium-Catalyzed Allylic Substitution with an Acyl Anion Equivalent: Stereospecific Construction of Acyclic Quaternary Carbon Stereogenic Centers

Enantioselective construction of triaryl-substituted all-carbon quaternary stereocenters via organocatalytic arylation of oxindoles with azonaphthalenes

Azonaphthalenes have been verified as a class of effective arylation reagents in a variety of asymmetric transformations. Here a highly efficient approach to construct triaryl-substituted all-carbon quaternary stereocenters through chiral phosphoric acid-catalyzed enantioselective arylation of 3-aryl-2-oxindoles with azonaphthalenes is disclosed. This chemistry is scalable and displays excellent functional group tolerance, furnishing a series of 3,3-disubstituted 2-oxindole derivatives in good yields with excellent enantiocontrol. Preliminary mechanistic data suggest that the initially formed direct addition intermediate undergoes intramolecular annulation under acidic reaction conditions.

Nickel-Catalyzed Direct Substitution of Allylic Alcohols with Nitriles: A General Tool for the Construction of Acyclic C2-Tertiary or Quaternary Benzyl Nitriles

A nickel-catalyzed direct reaction of allylic alcohols with benzyl nitrile derivatives has been developed. The method provides an efficient route for the synthesis of nitriles bearing an α-tertiary or quaternary carbon center in good to excellent yields with high regioselectivity, wide substrate scope, and functional group compatibility. BSA was identified as the effective additive for facilitating the coupling process mainly for alkyl allylic alcohols.

Visible light-initiated radical 1,3-difunctionalization of β,γ-unsaturated ketones

Radical-mediated 1,2-difunctionalization of olefins is a well-established synthetic technique widely used in the rapid construction of structurally diverse molecular entities. However, radical-mediated 1,3-difunctionalization reactions are rare, and the substrates are generally limited to strained skeletons. Here, we report a practical approach for 1,3-difunctionalization of available β,γ-unsaturated ketones via a radical cascade process including visible light-irradiated radical addition, thermodynamic stability-driven 1,2-carbonyl migration from unactivated all-carbon quaternary center, and terminal C-radical varied transformations. Various highly functionalized alkyl skeletons with different valuable functional groups at positions 1 and 3 and the carbonyl group at position 2 have been synthesized through a radical chain pathway or Cu-catalyzed Ritter-type reaction. Moreover, this protocol provides a real case of diversity-oriented radical rearrangement for drug discovery. We identified a previously unknown chemotype of dual inhibitors for hypoxia-inducible factor (HIF) and WNT signaling pathways from products. These small-molecule inhibitors could suppress HIF and WNT signaling-dependent HCT116 cell growth in 2D and 3D culture systems.

Organocatalytic enantioselective SN1-type dehydrative nucleophilic substitution: access to bis(indolyl)methanes bearing quaternary carbon stereocenters

A highly general and straightforward approach to access chiral bis(indolyl)methanes (BIMs) bearing quaternary stereocenters has been realized via enantioconvergent dehydrative nucleophilic substitution. A broad range of 3,3'-, 3,2'- and 3,1'-BIMs were obtained under mild conditions with excellent efficiency and enantioselectivity (80 examples, up to 98% yield and >99 : 1 er). By utilizing racemic 3-indolyl tertiary alcohols as precursors of alkyl electrophiles and indoles as C-H nucleophiles, this organocatalytic strategy avoids pre-activation of substrates and produces water as the only by-product. Mechanistic studies suggest a formal SN1-type pathway enabled by chiral phosphoric acid catalysis. The practicability of the obtained enantioenriched BIMs was further demonstrated by versatile transformation and high antimicrobial activities (3al, MIC: 1 μg mL-1).

Asymmetric Rhodium-Catalyzed Allylic Substitution Reactions with Nitrile-Stabilized Carbanions

This Account summarizes our recent work on rhodium-catalyzed allylic alkylation reactions with nitrile-stabilized carbanions. Despite the challenges associated with employing nitrile stabilized nucleophiles in transition-metal-catalyzed reactions, we recently developed both enantiospecific and enantioselective allylic alkylation reactions. Notably, these novel reactions permit the expedient and selective access to an array of acyclic ternary and quaternary stereogenic centers that are present in important biologically active molecules. 1 Introduction 2 Enantiospecific Reactions of Nitrile-Stabilized Anions 3 Enantioselective Reactions of Nitrile-Stabilized Anions 4 Conclusion

Copper-Catalyzed Hydroalumination of Allenes with Diisobutylaluminum Hydride: Synthesis of Allylic Ketones with α-Quaternary Centers via Tandem Allylation/Oppenauer Oxidation

An efficient and straightforward approach to allylaluminum reagent synthesis through Cu-catalyzed hydroalumination of readily accessible allenes with diisobutylaluminum hydride is described. The N-heterocyclic carbene-based copper complex promotes hydride addition to various functionalized allenes under mild reaction conditions. The catalytic reaction is applied to a highly selective one-pot synthesis of allylic ketones with α-tertiary and α-quaternary centers through tandem nucleophilic addition of in situ-generated allylaluminums to aldehydes/Oppenauer oxidation.

Catalytic enantioselective allene-anhydride approach to β,γ-unsaturated enones bearing an α-all-carbon-quarternary center

A protocol of highly regio- and enantioselective copper-catalyzed hydroacylation of the non-terminal C[double bond, length as m-dash]C bond in 1,1-disubstituted terminal allenes with anhydrides has been developed. Both aromatic and aliphatic carboxylic anhydrides are applicable to the efficient construction of all carbon quarternary centers connected with a versatile C[double bond, length as m-dash]C bond and a useful ketone functionality. The synthetic potentials of the enantioenriched products have also been demonstrated. Density functional theory (DFT) calculations were performed to explain the steric outcome of the products: the hydroacylation proceeds through a six-membered transition state and the ligand-substrate steric interactions account for the observed enantioselectivity although the chiral ligand is far away from the to-be-genetated chiral center.

Regioselective and Stereospecific Rhodium-Catalyzed Allylic Cyanomethylation with an Acetonitrile Equivalent: Construction of Acyclic β-Quaternary Stereogenic Nitriles

A highly regioselective and stereospecific rhodium-catalyzed cyanomethylation of tertiary allylic carbonates for the construction of acyclic β-quaternary stereogenic nitriles is described. This protocol represents the first example of a metal-catalyzed allylic substitution reaction using a triorganosilyl-stabilized acetonitrile anion, which permits access to several carbonyl derivatives that are challenging to prepare using conventional pronucleophiles. The synthetic utility of the stereospecific cyanomethylation is further exemplified through the construction of an intermediate utilized in the total synthesis of both (-)-epilaurene and (-)-α-cuparenone.

Promoting Thermodynamically Unfavorable [3,3] Rearrangements by Chemoselective Reduction

Herein described is a strategy for promoting thermodynamically unfavorable [3,3] Cope rearrangements. 3,3-Dicyano-1,5-dienes that are resistant to the thermal rearrangement can be promoted under reductive conditions. The reduced Cope products are versatile, bifunctional building blocks.

Palladium-catalyzed enantioselective decarboxylative allylic alkylation of fully substituted N-acyl indole-derived enol carbonates

The first enantioselective Pd-catalyzed decarboxylative allylic alkylation of fully substituted N-acyl indole-derived enol carbonates generates acyclic all-carbon quaternary stereocenters in excellent yields (up to 99%) and enantioselectivities (up to 98% ee) using a new electron-deficient phosphinoxazoline (PHOX) ligand.

The first enantioselective palladium-catalyzed decarboxylative allylic alkylation of fully substituted N-acyl indole-derived enol carbonates forming acyclic all-carbon quaternary stereocenters is reported. Excellent yields up to 99% and enantioselectivities up to 98% ee are obtained through the use of a new electron-deficient phosphinoxazoline (PHOX) ligand. Control of substrate enolate geometry is crucial for high selectivity. The obtained α-quaternary N-acyl indoles are formal ester equivalents, and represent a useful handle for further synthetic transformations.

Nickel-Catalyzed Decarboxylative Alkenylation of Anhydrides with Vinyl Triflates or Halides

Decarboxylative cross-coupling of aliphatic acid anhydrides with vinyl triflates or halides was accomplished via nickel catalysis. This methodology works well with a broad array of substrates and features abundant functional group tolerance. Notably, our approach addresses the issue of safe and environmental installation of methyl or ethyl group into molecular scaffolds. The method possesses high chemoselectivity toward alkyl groups when aliphatic/aromatic mixed anhydrides are involved. Furthermore, diverse ketones could be modified with our strategy.

Diastereoselective Rh-catalyzed decarboxylative allylation to form quaternary stereocenters using sulfinimine as the directing group

In this paper, we reported for the first time that the diastereoselective Rh-catalyzed decarboxylative allylation of chiral sulfinimines could be used to form quaternary stereocenters.

Phosphonate-Directed Catalytic Asymmetric Hydroboration: Delivery of Boron to the More Substituted Carbon, Leading to Chiral Tertiary Benzylic Boronic Esters

Phosphonate-directed catalytic asymmetric hydroboration (CAHB) of β-aryl/heteroaryl methylidenes and trisubstituted alkenes by pinacolborane enables facile access to functionalized, chiral tertiary benzylic boronic esters. Hydroboration is catalyzed by a chiral rhodium catalyst prepared in situ from a Rh(I)-precursor in combination with a simple TADDOL-derived chiral cyclic monophosphite in a 1:1 ratio. The regio- and stereochemistry arises from the combined effects of the relative disposition of the directing group to the alkene, the alkene substitution pattern, and the necessity of an aryl substituent attached to the alkene. A range of aryl and heteroaryl substituents can be accommodated, and for several chiral substrates, the reactions are efficiently catalyst-controlled enabling the choice of diastereomeric products as desired. Stereospecific transformations of the chiral boronic ester afford chiral phosphonates bearing a quaternary carbon stereocenter. The synthetic utility of the products is further demonstrated by α-oxidation of the phosphonate leading to hydroxy- and oxo-phosphonates; the latter readily undergo elimination/substitution reactions to unmask the phosphonate functionality with the formation of aldehydes, alcohols, esters, amides, acids and ketones.

Catalytic Enantioselective Synthesis of Acyclic Quaternary Centers: Palladium-Catalyzed Decarboxylative Allylic Alkylation of Fully Substituted Acyclic Enol Carbonates

The first enantioselective palladium-catalyzed decarboxylative allylic alkylation of fully substituted acyclic enol carbonates providing linear α-quaternary ketones is reported. Investigation into the reaction revealed that the use of an electron-deficient phosphinooxazoline ligand renders the enolate geometry of the starting material inconsequential, with the same enantiomer of product obtained in the same level of selectivity regardless of the starting ratio of enolates. As a result, a general method toward acyclic all-carbon quaternary stereocenters has been developed.

Catalytic asymmetric synthesis of geminal-dicarboxylates

Stereogenic acetals, spiroacetals and ketals are well-studied stereochemical features that bear two heteroatoms at a common carbon atom. These stereocenters are normally found in cyclic structures while linear (or acyclic) analogues bearing two heteroatoms are rare. Chiral geminal-dicarboxylates are illustrative, there is no current way to access this class of compounds while controlling the stereochemistry at the carbon center bound to two oxygen atoms. Here we report a rhodium-catalysed asymmetric carboxylation of ester-containing allylic bromides to form stereogenic carbon centers bearing two different carboxylates with high yields and enantioselectivities. The products, which are surprisingly stable to a variety of acidic and basic conditions, can be manipulated with no loss of enantiomeric purity as demonstrated by ring closing metathesis reactions to form chiral lactones, which have been extensively used as building blocks in asymmetric synthesis.

Cu-catalyzed enantioselective synthesis of tertiary benzylic copper complexes and their in situ addition to carbonyl compounds

Catalytic chemo- and enantioselective generation of tertiary benzylic copper complexes from Cu-B(pin) (pin = pinacolato) additions to 1,1-disubstituted alkenes followed by in situ reactions with ketones and carboxylic acid phenol esters to construct multifunctional alkylboron compounds that contain quaternary stereogenic centers is presented. The method is distinguished by the unprecedented reaction mode of tertiary benzylic Cu complexes, allowing reaction with a wide range of carbonyl electrophiles in good yields and with high chemo-, site-, diastereo- and enantioselectivity. The catalytic protocol was performed with easily accessible chiral ligands and copper salts at ambient temperature. Functionalization of multifunctional alkylboron products provides useful building blocks that are otherwise difficult to access.

Regio- and Enantioselective Rhodium-Catalyzed Allylic Alkylation of Racemic Allylic Alcohols with 1,3-Diketones

Highly regio- and enantioselective rhodium-catalyzed allylic alkylation of 1,3-diketones with racemic secondary allylic alcohols is reported. In the presence of a Rh-catalyst derived from the Carreira (P, olefin)-ligand and TFA as an additive, chiral branched α-allylated 1,3-diketones could be obtained in good to excellent yields, with excellent regio- and enantioselectivity ( b/ l > 19/1, 86-98% ee). The direct utilization of allyl alcohols as electrophiles represents an improvement from the viewpoint of an atom economy. Both aryl- and aliphatic-substituted allyl alcohols are suitable substrates with excellent reaction outcomes. This reaction features mild conditions, broad substrate scope, and readily available substrates.

Divergent synthesis of functionalized pyrrolidines and γ-amino ketones via rhodium-catalyzed switchable reactions of vinyl aziridines and silyl enol ethers

Rhodium-catalyzed enantiospecific intermolecular [3+2] cycloadditions and ring-opening reactions of vinylaziridines with silyl enol ethers have been developed to synthesize functionalized pyrrolidines and γ-amino ketones, respectively.

Divergent Access to Functionalized Pyrrolidines and Pyrrolines via Iridium-Catalyzed Domino-Ring-Opening Cyclization of Vinyl Aziridines with β-Ketocarbonyls

A useful synthesis of five-membered N-heterocycles has been developed through an iridium-catalyzed domino-ring-opening cyclization of vinylaziridines with β-ketocarbonyls. α-Substituted 1,3-dicarbonyls reacted with vinylaziridines to give 2-methylenepyrrolidines bearing two adjacent sp³-carbon centers with moderate to excellent diastereoselectivity, while the reaction of α-unsubstituted 1,3-dicarbonyls afforded 2-pyrrolines in good yield.

Regio- and stereospecific rhodium-catalyzed allylic alkylation with an acyl anion equivalent: an approach to acyclic α-ternary β,γ-unsaturated aryl ketones

The regio- and stereospecific rhodium-catalyzed allylic alkylation of secondary allylic carbonates with cyanohydrin pronucleophiles facilitates the direct construction of acyclic α-ternary β,γ-unsaturated aryl ketones. Interestingly, this study illustrates the impact of deaggregating agents on regiocontrol and the electronic nature of the aryl component to suppress olefin isomerization. In addition, we demonstrate that the dimethylamino substituent, which modulates the pKa of the α-ternary β,γ-unsaturated aryl ketone, provides a useful synthetic handle for further functionalization via Kumada cross-coupling of the aryl trimethylammonium salt. Finally, the stereospecific alkylation of a chiral nonracemic secondary allylic carbonate affords the enantioenriched α-ternary aryl ketone, which was employed in a formal synthesis of trichostatic acid to illustrate that the allylic alkylation proceeds with net retention of configuration.

Synthesis of α-Quaternary Formimides and Aldehydes through Umpolung Asymmetric Copper Catalysis with Isocyanides

A highly regio- and enantioselective copper-catalyzed three-component coupling of isocyanides, hydrosilanes, and γ,γ-disubstituted allylic phosphates/chlorides to afford chiral α-quaternary formimides was enabled by the combined use of our original chiral naphthol-carbene ligand as a functional Cu-supporting ligand and LiOtBu as a stoichiometric Lewis base for Si. The formimides were readily converted to α-quaternary aldehydes.

Regio- and Enantioselective Rhodium-Catalyzed Addition of 1,3-Diketones to Allenes: Construction of Asymmetric Tertiary and Quaternary All Carbon Centers

An unprecedented highly regio- and enantioselective rhodium-catalyzed addition of 1,3-diketones to terminal and 1,1-disubstituted allenes furnishing asymmetric tertiary and quaternary all-carbon centers is reported. By applying a Rh^I /phosphoramidite/TFA catalytic system under mild conditions, the desired chiral branched α-allylated 1,3-diketones could be obtained in good to excellent yields, with perfect regioselectivity and in high enantioselectivity. The reaction shows a broad functional-group tolerance on both reaction partners highlighting its synthetic potential.

Full chirality transfer in the synthesis of hindered tertiary boronic esters under in situ lithiation-borylation conditions

Hindered tertiary neopentyl glycol boronic esters can be prepared by using in situ lithiation-borylation of enantiopure secondary benzylic carbamates at -20 °C with full chirality transfer.

Tandem Rh-catalysis: decarboxylative β-keto acid and alkyne cross-coupling

Herein, we describe a regioselective Rh-catalyzed decarboxylative cross-coupling of β-keto acids and alkynes to access branched γ,δ-unsaturated ketones. Rh-hydride catalysis enables the isomerization of an alkyne to generate a metal-allyl species that can undergo carbon-carbon bond formation. Ketones are generated under mild conditions, without the need for base or activated electrophiles.

An efficient approach for the construction of trifluoromethylated all-carbon quaternary stereocenters: enantioselective Ni(ii)-catalyzed Michael addition of 2-acetyl azaarene to β,β-disubstituted nitroalkenes

Michael addition of 2-acetyl azaarenes with β,β-disubstituted nitroalkenes afforded chiral compounds in good yields and with excellent enantioselectivities.

Regioselective Rhodium-Catalyzed Addition of 1,3-Dicarbonyl Compounds to Terminal Alkynes

A new method for the rhodium-catalyzed regioselective C-C bond formation using terminal alkynes and 1,3-dicarbonyl compounds to achieve valuable branched α-allylated 1,3-dicarbonyl products is reported. With a Rh(I)/DPEphos/p-CF3-benzoic acid as the catalyst system, the desired products can be obtained in good to excellent yields and with perfect regioselectivity. A broad range of functional groups were tolerated, and first experimental insights of a plausible reaction mechanism were obtained.

All-Carbon [3+3] Oxidative Annulations of 1,3-Enynes by Rhodium(III)-Catalyzed C-H Functionalization and 1,4-Migration

1,3-Enynes containing allylic hydrogens cis to the alkyne function as three-carbon components in rhodium(III)-catalyzed, all-carbon [3+3] oxidative annulations to produce spirodialins. The proposed mechanism of these reactions involves the alkenyl-to-allyl 1,4-rhodium(III) migration.

Stereoselective reaction of 2-carboxythioesters-1,3-dithiane with nitroalkenes: an organocatalytic strategy for the asymmetric addition of a glyoxylate anion equivalent

Under mild reaction conditions γ-nitro-β-aryl-α-keto esters with up to 92% ee were obtained, realizing a formal catalytic stereoselective conjugate addition of the glyoxylate anion synthon.