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An intriguing Bronsted acid-catalyzed 1,6-hydrophosphination of in situ generated propargylic para-quinone methides (p-QMs) and aza-para-quinone methides (aza-p-QMs) with H-phosphorus oxides via dehydration/1,6-addition under ultrasonic irradiation is described. This methodology provides a rapid and green approach for the construction of diarylmethyl phosphorus oxides bearing phosphorus-substituted quaternary carbon centers in high yields (up to 98% yield) within merely 5 ​min. This environmentally benign protocol represents a unique example of 1,6-conjugate additions of propargylic p-QMs and aza-p-QMs for site-selective C–P bond formation in an operationally simple and atom-economical manner. The use of readily available Bronsted acid catalyst, operationally simplicity, high yields, and high atom economy make this protocol very facile, practical, easily scaled-up and environmentally friendly.

A novel iodine promoted cyclization of enaminone with aryl methyl ketones has been developed as a straightforward method for constructing 2-hydroxy-pyrrol-3(2H)-ones. This strategy affords structurally diverse 2-hydroxy-pyrrol-3(2H)-ones rings in high yields. Moreover, a quarternary alcohol has been constructed efficiently in the reaction. Product purification required only washing with CH2Cl2 solvent, thereby avoiding traditional chromatography and recrystallization, making this an example of group-assisted purification chemistry.

A novel, versatile approach for the synthesis of unsymmetrical 3,3'-diindolylmethanes (DIMs) with a quaternary carbon center has been developed via iodine-catalyzed coupling of trifluoromethyl(indolyl)phenylmethanols with indoles. In contrast to previously reported methods, the new procedure is characterized by chemoselectivity, mild conditions, high yields, and scalability to obtain gram amounts for biological studies. Selected compounds were found to display affinity for cannabinoid receptors, which are promising drug targets for the treatment of inflammatory and neurodegenerative diseases.

A palladium-catalyzed allenamide carbopalladation/allylation with active methine compounds has been developed. Various indoles and isoquinolinones bearing a quaternary carbon center were achieved with good efficiency, a broad substrate scope and good functional group tolerance. This reaction underwent cascade oxidative addition, carbopalladation, and allylic alkylation, and two new C-C bonds were formed in one pot.

Hydroaminocarbonylation of alkenes is one of the most promising yet challenging methods for the synthesis of amides. Herein, we reported the development of a novel and effective Pd-catalyzed Markovnikov hydroaminocarbonylation of 1,1-disubstituted or 1,1,2-trisubstituted alkenes with aniline hydrochloride salts to afford amides bearing an α quaternary carbon. The reaction makes use of readily available starting materials, tolerates a wide range of functional groups, and provides a facile and straightforward approach to a diverse array of amides bearing an α quaternary carbon. Mechanistic investigations suggested that the reaction proceeded through a palladium hydride pathway. The hydropalladation and CO insertion are reversible, and the aminolysis is probably the rate-limiting step.

Reductive cyanation of tertiary alkyl bromides using electrophilic cyanating reagent and zinc reductant was developed, providing various α-cyano ketones, esters, and carboxamides containing a nitrile-bearing all-carbon quaternary center in good to excellent yields under mild reaction conditions. The corresponding reaction mechanism involving in situ generated organozinc reagent and reactivity distinction was elucidated by density functional theory computation.

A palladium-catalyzed allylic alkylation dearomatization of β-naphthols and indoles with gem-difluorinated cyclopropanes has been developed. This reaction provided an efficient route to access 2-fluoroallylic β-naphthalenones and indolenines bearing quaternary carbon centers in good yields with high Z-selectivity via C-C bond activation, C-F bond cleavage and the dearomatization process, benefiting from the wide substrate scope and good functional group tolerance. Moreover, 2-fluoroallylic furanoindoline and pyrroloindolines were achieved in good efficiency via cascade allylic alkylation, dearomatization and cyclization processes in the presence of Et3B.

A nickel-catalyzed hydrocyanation of aliphatic allenes with excellent regioselectivity is developed. This protocol features mild reaction conditions and good functional group tolerance, providing an efficient catalytic pathway to access various allylic nitriles containing quaternary carbon centers in a one-step fashion. In addition, preliminarily attempts were made to investigate an asymmetric version of this reaction.

A cobalt-catalyzed domino Pauson–Khand and [4 + 2] cycloaddition of substituted diynes has been developed for the rapid construction of complexed polycyclic ring systems. Using benzene-1,3,5-triyl triformate (TFBen) as the CO source, the reaction proceeded well to give various tetracyclic compounds bearing two new quaternary carbon cores in high yields with excellent regioselectivity and diastereoselectivity. Control experiments were performed to gain a better understanding of the reaction mechanism.

Bismuth(iii)-catalyzed regioselective functionalization at the C-6 position of tetrahydroquinolines and the C-5 position of indolines has been demonstrated. For the first time, one pot symmetrical and unsymmetrical arylation of isatins with tetrahydroquinolines was accomplished giving a completely new product skeleton in good to excellent yields. Most importantly, this protocol leads to the formation of a highly strained quaternary carbon stereogenic center, which is a challenging task. Benzhydryl and 1-phenylethyl trichloroacetimidates have been used as the alkylating partners to functionalize the C-6 and C-5 positions of tetrahydroquinolines and indolines, respectively. The scope of the developed methodology has been extended for the synthesis of the bioactive CYP19-inhibitor and its analogue.

The development of highly effective chiral ligands is a key topic in enhancing the catalytic activity and selectivity in metal-catalyzed asymmetric synthesis. Traditionally, the difficulty of ligand synthesis, insufficient accuracy in controlling the stereoselectivity, and poor universality of the systems often become obstacles in this field. Using the concept of nonequivalent coordination to the metal, our group has designed and synthesized a series of new chiral catalysts to access various carbon/silicon and/or multiple stereogenic centers containing products with excellent chemo-, diastereo-, and enantioselectivity.In this Account, we summarize a series of new phosphine ligands with multiple stereogenic centers that have been developed in our laboratory. These ligands exhibited good to excellent performance in the transition-metal-catalyzed enantioselective construction of quaternary carbon/silicon and multiple stereogenic centers. In the first section, notable examples of the design and synthesis of new chiral ligands by non-covalent interaction-based multisite activation are described. The integrations of axial chirality, atom-centered chirality, and chiral anions and multifunctional groups into a single scaffold are individually highlighted, as represented by Ar-BINMOLs and their derivative ligands, HZNU-Phos, Fei-Phos, and Xing-Phos. In the second, third, and fourth sections, the enantioselective construction of quaternary carbon stereocenters, multiple stereogenic centers, and silicon stereogenic centers using our newly developed chiral ligands is summarized. These sections refer to detailed reaction information in the chiral-ligand-controlled asymmetric catalysis based on the concept of nonequivalent coordination with multisite activation. Accordingly, a wide array of transition metal and main-group metal catalysts has been applied to the enantioselective synthesis of chiral heterocycles, amino acid derivatives, cyclic ketones, alkenes, and organosilicon compounds bearing one to five stereocenters.This Account shows that this new model of multifunctional ligand-controlled catalysts exhibits excellent stereocontrol and catalytic efficiency, especially in a stereodivergent and atom-economical fashion. Furthermore, a brief mechanistic understanding of the origin of enantioselectivity from our newly developed chiral catalyst systems could inspire further development of new ligands and enhancement of enantioselective synthesis by asymmetric metal catalysis.

We have developed a nickel- nickel/bisphosphine-catalyzed stereoconvergent cross-coupling reaction of epoxides with alkenylboronic acids. Racemic spiroepoxyoxindoles were converted to chiral homoal...

We report a Ni-catalyzed regioselective α-carbonylalkylarylation of vinylarenes with α-halocarbonyl compounds and arylzinc reagents. The reaction works with primary, secondary, and tertiary α-halocarbonyl molecules, and electronically varied arylzinc reagents. The reaction generates γ,γ-diarylcarbonyl derivatives with α-secondary, tertiary, and quaternary carbon centers. The products can be readily converted to aryltetralones, including a precursor to Zoloft, an antidepressant drug.

Starting from diverse alkene-tethered aryl iodides and O-benzoyl-hydroxylamines, the enantioselective reductive cross-electrophilic 1,2-carboamination of unactivated alkenes was achieved using a chiral pyrox/nickel complex as the catalyst. This mild, modular, and practical protocol provides rapid access to a variety of β-chiral amines with an enantioenriched aryl-substituted quaternary carbon center in good yields and with excellent enantioselectivities. This process reveals a complementary regioselectivity when compared to Pd and Cu catalysis.

A strategy for the synthesis of cis-hydrocarbazole with a C3 quaternary carbon center has been developed through nickel/Lewis acid dual-catalyzed arylcyanation. A wide array of cis-hydrocarbazoles was accessed with high diastereoselectivities and atom economies in a good yield. The rich chemistry of the installed nitrile group was demonstrated in the preparation of tryptamine- and tryptophol-derived cis-hydrocarbazoles.

Overcoming the inherent difficulty to prepare quaternary carbon stereogenic centers, the diastereo- and enantioselective preparation of acyclic carbon backbones possessing vicinal quaternary and tertiary stereogenic centers (i.e. in a 1,2-relationship) causes distorted geometries and represents a very acute problem in organic synthesis. Several approaches are discussed in this minireview underlining the challenges illustrated by the rather limited number of approaches available to practitioners.

A novel Pd(II)-catalyzed reductive asymmetric cyclization of N-tosyl-tethered 1,7-enynes using ethanol as a hydrogen source is reported. This reaction provides facile ways for the synthesis of two types of 1,2,3,4-tetrahydroquinolines possessing a chiral quaternary carbon center in high yields with excellent enantioselectivities. The obtained products can also be converted to other chiral functionalized tetrahydroquinolines efficiently. The procedure involves a palladium-catalyzed intramolecular hydropalladation/1,4-addition or β-heteroatom elimination cascade process.

Controlling the reactive species during the synthesis of complex aliphatic chains containing a quaternary carbon is incredibly difficult. In this paper, we efficiently controlled both radical and c...

Nickel-catalyzed desymmetric hydrogenation has been achieved. With the Ni(OTf)2/(S,S)-Ph-BPE system, a series of γ,γ-disubstituted cyclohexadienones were transformed to the corresponding cyclohexenones with a chiral all-carbon quaternary center at the γ position in high yields (92-98%) and excellent enantioselectivities (92%-99% ee). This catalytic system can also tolerate the desymmetric reaction of spirocarbocyclic cyclohexadienones to produce the corresponding cyclohexenones bearing a chiral spiro quaternary carbon with high yields (94%-98%) and ee values (96%-99% ee). Furthermore, this methodology provides an efficient and concise synthetic route to the intermediate of natural products cannabispirenones A and B.

A Cu-catalyzed protocol for cross-dehydrogenative coupling of benzofuranones with quinolines, indoles, carbazoles, and thiophene, which furnishes highly functionalized 3,3-diaryl benzofuranones bearing a three aryl quaternary carbon center at the C3 position in good yields, has been developed. A radical mechanism is proposed.

Trifluoromethylated chiral quaternary stereogenic carbon center at 2-position of thiochromans has been constructed through organocatalyzed Michael-aldol reaction. With quinine squaramide as catalyst, the reaction of 2-mercaptobenzaldehyde with β-aryl-β-CF3 enones or β-alkyl-β-CF3 enones gave 2-CF3-thiochromans bearing three contiguous stereogenic centers in good to excellent diastereoselectivities, enantioselectivities, and yields.

A palladium-catalyzed intramolecular carboborylation of 1, 3-diene has been developed for the synthesis of iminoindolines with a quaternary carbon centre. This method was applied to a substrate bearing several functional groups to afford a complex iminoindoline, which was subsequently converted into an ABCD ring model compound of communesins via an intramolecular Friedel–Crafts-type reaction.

A highly enantioselective cobalt-catalyzed reverse prenylation of β-ketoester with tertiary allylic carbonate to construct vicinal all-carbon quaternary carbon centers has been developed. By using the cobalt/( S, S)Ph-BPE complex generated in situ with zinc reduction, excellent branched to linear selectivity (20:1) and up to 92% ee have been obtained.

Microwave-assisted tertiary carbon radical reaction was developed. The reaction of tertiary xanthates with electron deficient alkenes was prompted by microwave irradiation, and various coupling products possessing quaternary carbon centers were obtained in good yields. The reaction was conducted under simple and common radical condition except for microwave irradiation, and the reaction completes within 5 min.

In this report, a palladium catalyzed direct trisallylation of azoles with alkyne via a novel subsequent mono C(sp2)–H allylation/olefin isomerization/y-selective double C(sp3)–H allylation process was developed. A wide range of substituted trisallylated azoles bearing all quaternary carbon centers has been synthesized efficiently and with high atom economy.

Demonstrated herein is the construction of trifluoromethylated quaternary carbon centers by an asymmetric radical transformation. Enantioenriched trifluoromethylated oxindoles were accessed using a hypervalent iodine-based trifluoromethyl transfer reagent in combination with a magnesium Lewis acid catalyst and PyBOX-type ligands to achieve up to 99 % ee and excellent chemical yields. Mechanistic studies were performed by experimental and computational methods and suggest a single-electron transfer induced SN2-type mechanism. This example is thereby the first report on the construction of enantioenriched trifluoromethylated carbon centers using hypervalent iodine-based reagents proceeding through such a reaction pathway. ISSN:1433-7851 ISSN:1521-3773 ISSN:0570-0833

Recent advances in Cpx MIII catalysis (M=Co, Rh, Ir) have enabled a variety of enantioselective C(sp2 )-H functionalization reactions, but enantioselective C(sp3 )-H functionalization is still largely unexplored. We describe an asymmetric C(sp3 )-H amidation of thioamides using an achiral CoIII /chiral carboxylic acid hybrid catalytic system, which provides easy and straightforward access to chiral β-amino thiocarbonyl and β-amino carbonyl building blocks with a quaternary carbon stereocenter.

Herein, we describe the formation of quaternary carbon centers with excellent diastereoselectivity via a strain-release protocol. An organometallic species is generated by Cp*Rh(III)-catalyzed C-H activation, which is then coupled with strained bicyclobutanes (BCBs) and a prochiral carbon electrophile in a three-component reaction. This work illustrates a rare example of BCBs in transition metal catalysis and demonstrates their broad potential to access novel reaction pathways. The method developed exhibits ample functional group tolerance, and the products can be further transformed into valuable α-quaternary β-lactones. Preliminary mechanistic investigations suggest a twofold C-C bond cleavage sequence involving σ-bond insertion and an ensuing β-carbon elimination event.

An enantioselective Pd(II)-catalyzed amino-cyclization and desymmetrizing nitrile addition cascade reaction of alkyne-tethered malononitriles is reported. This reaction forms two rings and one quaternary carbon center in a single step and serves as an efficient strategy for the construction of α-quaternary carbazolones with high enantioselectivities (up to 98:2 er). The utility of this method is demonstrated by product derivatization into a diverse array of heterocycles and a nitrile-containing leucomidine A analog.

A highly enantioselective allylic alkylation of isoquinolinedione derivatives under palladium catalysis was developed in the preparation of quaternary carbon stereocenters. Under standard reaction conditions, excellent yields and enantioselectivities were realized and the products could be transformed into dihydroisoquinolone with vicinal chiral carbon centers or THIQ core structures in short steps with high yields.

A method has been developed for the α-tertiary alkylation of zirconium enolates of N-(arylacetyl)oxazolidinones. This reaction directly installs an all-carbon quaternary center vicinal to a benzylic tertiary carbon in a highly diastereoselective manner.

Unprecedented α‐oxygenated β,γ‐unsaturated ketones bearing a quaternary carbon at the α‐position were synthesized in two steps from readily available α,β‐unsaturated ketones. The compounds were prepared on a gram scale under mild conditions via a key rearrangement step catalysed by 1 mol% of p‐toluenesulfonic acid as a low‐priced and sustainable catalyst. The olfactory properties of this novel family of odorants as well as of some derivatives have been assessed, revealing a quite broad odour spectrum and a pronounced susceptibility of the olfactory properties towards structural changes.

Herein we report the first palladium(0)-catalyzed asymmetric allylic alkylation (AAA) of allyl enol ether via π-allylpalladium intermediate using Trost chiral diphosphine. This unprecedented reaction produced very rare α-aryl quaternary aldehydes with multi-functional groups. The main novelty in the chemistry demonstrates that enol ethers can be used as precursors for π-allylpalladium intermediates, an observation that is certainly rare and to the best of our knowledge, perhaps without prior precedent. Chiral ligand (R,R)-L3 was found to be optimal in this Pd-AAA reaction and provided good to excellent yield (80–95%) and enantioselectivity (70–90%) with a range of analogs.

An asymmetric strategy for the construction of chiral sulfur-containing spirooxindole-fused heterocycles was achieved via a rhodium(II)/chiral phosphoric acid-cocatalyzed reaction between 2-mercaptophenyl ketones and 3-diazooxindoles. With this method, a series of spirooxindole-thiaindan derivatives bearing two contiguous quaternary carbon stereogenic centers were obtained in high yields with high diastereoselectivities and high-to-excellent enantioselectivities.

A novel nickel-catalyzed remote arylation of alkenyl aldehydes triggered by radical alkylation with tertiary α-carbonyl alkyl bromides is described, thus producing a quaternary carbon center containing ketones in promising yields with broad functional group compatibility. Preliminary mechanistic studies suggest that the combination of a 1,n-HAT (n = 5 or 6) from alkyl radicals to aldehyde C-H bonds with nickel catalysis may account for the realization of this reaction.

A novel synthesis of α-CF3 and α-CF2H amines via the aminofluorination of gem-difluoroalkenes and mono-fluoroalkenes, respectively, is reported. The method employs Selectfluor as an electrophilic fluorine source and acetonitrile as a nitrogen source. Mechanistic studies revealed a single-electron oxidation/fluorine-abstraction/Ritter-type amination pathway. The protocol allowed the synthesis of a broad range of fluorinated amines including those bearing quaternary carbon centers with good efficiency and functional group tolerance.

Enantioselective α-allylation of α-substituted β-ketoesters with simple allyl alcohols was successfully performed by synergistic catalysis with the catalyst combination of a chiral primary amino acid and an achiral palladium complex without additional promotors like acids or bases. The allylation reaction and generation of a chiral quaternary carbon stereocenter proceeded smoothly to produce α,α-disubstituted β-ketoesters in high yields (91-99%) with high enantioselectivities (90-99% ee).

Palladium-catalyzed multicomponent reactions (MCRs) between o-alkynylanlines, aryl iodides, and atmospheric pressure of CO2 are developed, affording a series of 3,3-diaryl 2,4-quinolinediones bearing a newly constructed quaternary carbon center in moderate to excellent yields. The reaction proceeded with a sequential carboxylation, trans-oxopalladation of C≡C bond by ArPdX species, and reductive elimination procedure leading to benzoxazine-2-ones bearing tetrasubstituted vinyl fragments. Then, rearrangement of benzoxazine-2-ones took place toward 3,3-diaryl 2,4-quinolinediones. This procedure features simultaneous formation of four bonds in one pot.

A Cp*RhIII -catalyzed annulative carbooxygenation of challenging 1,1-disubstituted alkenes triggered by C-H activation of N-aryloxyacetamides has been established, which affords 2,3-dihydrobenzofuran derivatives with a quaternary carbon center in good to excellent yields under mild redox-neutral conditions. An amide group on the alkenes is essential for the process, and may inhibit the β-H elimination from C(sp3)-Rh species by saturating the rhodium center through coordination. Furthermore, mechanistic insights obtained from control experiments suggest a mechanism involving a RhIII -RhV -RhIII catalytic cycle.

β-Ketonitriles bearing a quaternary carbon at the 2-position were prepared through Rh-catalyzed addition of aryl boronic acids to 2,2-disubstituted malononitriles. In contrast to the previously described transnitrilative cyanation of aryl boronic acids with dialkylmalononitriles, the present reaction avoids retro-Thorpe collapse of the intermediate addition product through the use of a milder base. The reaction was amenable to a variety of aryl boronic acids and disubstituted malononitriles, providing a diverse array of β-ketonitriles. The products could be further derivatized to valuable chiral α,α-disubstituted-β-aminonitriles through addition reactions to the corresponding N-tert-butanesulfinyl imines.

Herein, rhodium(III)-catalyzed C-H activation/subsequent [4 + 1] cyclization reactions between benzamides and propargyl alcohols are reported in which propargyl alcohols serve as unusual one-carbon units. This title transformation led to a series of isoindolinones bearing a quaternary carbon with moderate to good yields without the requirement for external metal oxidants. Due to the mild and simple reaction conditions, this reaction is compatible with various functional groups.

A new cascade process has been accomplished for the synthesis of tetrahydro-1H-cyclopenta[c]furans through palladium-catalyzed [2 + 2 + 1] cyclization of 1,6-enynes with vinyl bromides. Notably, the key feature of this transformation is the use of vinyl bromides as the C1 building block. Various functionalized tetrahydro-1H-cyclopenta[c]furans bearing two quaternary carbon centers could be obtained in good yields with excellent diastereoselectivities.

A copper-catalyzed cyanothiolation of N-tosylhydrazones with thiocyanates to generate α-arylthioalkanenitriles bearing sulfur-substituted quaternary carbon center atoms has been achieved., Sulfur-containing nitriles have important research value in the life sciences due to their diverse biological activities resulting from the sulfur and cyano functional groups. Herein, a copper-catalyzed cyanothiolation of N-tosylhydrazones with thiocyanates to generate α-arylthioalkanenitriles bearing sulfur-substituted quaternary carbon center atoms has been described. This novel protocol involves the procedure of copper carbene species promoting S–CN bond cleavage and C–CN/C–S bond reconstruction to introduce both sulfur and cyano groups onto a single carbon center. This cyanothiolation reaction will greatly enhance the synthetic utility of carbenoid species as new entries for the construction of diverse heteroatom-containing nitriles via cyanofunctionalization of metal–carbene species.

Determination of the absolute configuration of chiral tetra-substituted carbon centers is one of the most taxing steps in the enantioselective construction of this structural motif in asymmetric synthesis. Here, we demonstrate that the crystalline sponge method provides an effective way to crystallographically determine the absolute configuration of organic compounds bearing chiral quaternary carbons (including tetra-substituted ones) that are synthesized by recently developed enantioselective catalytic reactions.

We report a Pd-catalyzed arylative dearomatization/ring expansion cascade of furfurylcyclobutanols that involves a spiro π-allyl palladium intermediate and affords structurally novel dispirooxindoles containing two quaternary carbon centers in good yields with high step economy, diastereospecificity, and enantioselectivity.

Rhodium(III)-catalyzed annulative coupling of sulfoxonium ylides with allenoates was achieved, forming highly functionalized cyclopropanes with a quaternary carbon center by means of the sulfoxonium ylide functionality as a traceless bifunctional directing group and C4 synthon via an arene C-H activation and cyclopropanation cascade. The protocol features simultaneous formation of three new C-C bonds in one pot with excellent diastereoselectivity. The resultant cyclopropanation products could be further transformed to diverse synthetically useful compounds.

This work emphasizes the synthesis of alkyl esters via Cu-catalyzed and In-mediated alkoxycarbonylation of unactivated alkyl iodides in the presence of In or InI. The reactions were suitable for the preparation of primary, secondary, and even tertiary alkyl esters, representing an exceptionally rare example for the creation of quaternary carbon centers upon formation of esters. The preliminary mechanistic studies indicated that alkyl radicals were involved, and Cu/In/CO played a cooperative role in the carbonylation event.

In this study, the highly enantioselective α-allylation of α-substituted β-ketoesters, particularly 2-oxocycloalkanecarboxylates, is achieved by synergistic catalysis with an achiral palladium complex and a chiral primary amino acid. Various α-allylated β-ketoesters containing a quaternary carbon stereogenic center are synthesized in high yields (up to 97%) with excellent enantioselectivity (up to 99% ee).

A rhodium-catalyzed oxidative amidation reaction has been developed with sterically hindered aldehydes and alcohols for the synthesis of amides containing a quaternary carbon at the α position. A variety of amine nucleophiles, both aliphatic and aromatic, are employed and afford the corresponding amides in good to excellent yields. Finally, mechanistic studies are performed to gain insight into both catalytic cycles.