A Powerful Chiral Counterion Strategy for Asymmetric Transition Metal Catalysis

Palladium-catalyzed cross-coupling of alcohols with olefins by positional tuning of a counteranion

Transition metal-catalyzed cross-couplings have great potential to furnish complex ethers; however, challenges in the C(sp3)-O functionalization step have precluded general methods. Here, we describe computationally guided transition metal-ligand design that positions a hydrogen-bond acceptor anion at the reactive site to promote functionalization. A general cross-coupling of primary, secondary, and tertiary aliphatic alcohols with terminal olefins to furnish >130 ethers is achieved. The mild conditions tolerate functionality that is prone to substitution, elimination, and epimerization and achieve site selectivity in polyol settings. Mechanistic studies support the hypothesis that the ligand's geometry and electronics direct positioning of the phosphate anion at the π-allyl-palladium terminus, facilitating the phosphate's hydrogen-bond acceptor role toward the alcohol. Ligand-directed counteranion positioning in cationic transition metal catalysis has the potential to be a general strategy for promoting challenging bimolecular reactivity.

Rhodium-Catalyzed Enantioselective Intramolecular Hydroalkoxylation of Allenes and Application in the Total Synthesis of (R,R,R)-α-Tocopherol

We report herein of a novel, enantioselective and rhodium- catalyzed cyclisation of allenyl alcohols towards chiral α-vinylic, cyclic ethers employing a rhodium/(R,R)-Me-ferrocelane catalyst. The corresponding chiral cyclic products were obtained in general high yields and enantioselectivities. The synthetic value of our obtained products was further exemplified by transformations of the allylic ether function. Furthermore, applying our newly developed method in our previously reported route towards the total synthesis of (R,R,R)-α-tocopherol, we accomplished a significantly improved 2nd generation synthesis of the chromane building providing a total number of 13 steps and an overall total yield of 27 %.

Diffusion Nuclear Magnetic Resonance Measurements on Cationic Gold (I) Complexes in Catalytic Conditions: Counterion and Solvent Effects

The amount of free ions, ion pairs, and higher aggregate of the possible species present in a solution during the gold(I)-catalyzed alkoxylation of unsaturated hydrocarbon, i.e., ISIP (inner sphere ion pair) [(NHC)AuX] and OSIP (outer sphere ion pairs) [(NHC)Au(TME)X] [NHC 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; TME = tetramethylethylene (2,3-bis methyl-butene); X- = Cl-, BF4-, OTf-; and OTs- BArF4- (ArF = 3,5-(CF3)2C6H3)], has been determined. The 1H and 19F DOSY NMR measurements conducted in catalytic conditions indicate that the dissociation degree (α) of the equilibrium ion pair/free ions {[(NHC)Au(TME)X] [(NHC)Au(TME)]+ + X-} depends on the nature of the counterion (X-) when chloroform is the catalytic solvent: while the compounds containing OTs- and OTf- as the counterion gave a low α (which means a high number of ion pairs) of 0.13 and 0.24, respectively, the compounds containing BF4- and BArF4- showed higher α values of 0.36 and 0.32, respectively. These results experimentally confirm previous deductions based on catalytic and theoretical data: the lower the α value, the greater the catalytic activity because the anion that can activate methanol during a nucleophilic attack, although the lower propensity to activate methanol of BF4- and BArF4-, as suggested by the DFT calculations, cannot be completely overlooked. As for the effect of the solvent, α increases as the dielectric constant increases, as expected, and in particular, green solvents with high dielectric constants show a very high α (0.90, 0.84, 0.80, and 0.70 for propylene carbonate, γ-valerolactone, acetone, and methanol, respectively), thus confirming that the moderately high activity of NHC-Au-OTf in these solvents is due to the specific effect of polar functionalities (O-H, C=O, O-R) in activating methanol. Finally, the DOSY measurements conducted in p-Cymene show the formation of quadrupole species: under these conditions, the anion can better exercise its 'template' and 'activating' roles, giving the highest TOF.

Enantioselective Divergent Syntheses of Diterpenoid Pyrones

Capitalizing a synergy between late-stage C(sp3)-H alkynylation and a series of transition metal-catalyzed alkyne functionalization reactions, we reported herein enantioselective divergent synthesis of 10 diterpenoid pyrones within 14-16 steps starting from chiral pool enoxolone, including the first enantioselective synthesis of higginsianins A, B, D, E, and metarhizin C. Our synthesis also highlights an unprecedented biomimetic oxidative rearrangement of α-pyrone into 3(2H)-furanone, as well as applications of Echavarren C(sp3)-H alkynylation reaction and Toste chiral counterion-mediated Au-catalyzed intramolecular allene hydroalkoxylation in natural product synthesis.

Pd-catalyzed divergent regioselective annulation of phosphinyl allenes accessing polyarylfurans and 2H-chromenes

A novel and efficient regioselective annulation of phosphinyl allenes with 2-bromophenol or 1-bromo-2-naphthol is achieved by palladium catalysis. The divergent pathway delivers structurally diverse polyarylfurans and 2H-chromene skeletons via two different Heck-type annulations. This protocol represents regioselectivity-tunable transformation of allenes into functionalized O-containing heterocycles with excellent group compatibility.

Cinchona-Based Hydrogen-Bond Donor Organocatalyst Metal Complexes: Asymmetric Catalysis and Structure Determination

In this study, we describe the synthesis of cinchona (thio)squaramide and a novel cinchona thiourea organocatalyst. These catalysts were employed in pharmaceutically relevant catalytic asymmetric reactions, such as Michael, Friedel-Crafts, and A3 coupling reactions, in combination with Ag(I), Cu(II), and Ni(II) salts. We identified several organocatalyst-metal salt combinations that led to a significant increase in both yield and enantioselectivity. To gain insight into the active catalyst species, we prepared organocatalyst-metal complexes and characterized them using HRMS, NMR spectroscopy, and quantum chemical calculations (B3LYP-D4/def2-TZVP), which allowed us to establish a structure-activity relationship.

Valence-isomer selective cycloaddition reaction of cycloheptatrienes-norcaradienes

The rapid and precise creation of complex molecules while controlling multiple selectivities is the principal objective in synthetic chemistry. Combining data science and organic synthesis to achieve this goal is an emerging trend, but few examples of successful reaction designs are reported. We develop an artificial neural network regression model using bond orbital data to predict chemical reactivities. Actual experimental verification confirms cycloheptatriene-selective [6 + 2]-cycloaddition utilizing nitroso compounds and norcaradiene-selective [4 + 2]-cycloaddition reactions employing benzynes. Additionally, a one-pot asymmetric synthesis is achieved by telescoping the enantioselective dearomatization of non-activated benzenes and cycloadditions. Computational studies provide a rational explanation for the seemingly anomalous occurrence of thermally prohibited suprafacial [6 + 2]-cycloaddition without photoirradiation.

Enantioselective merged gold/organocatalysis

Gold complexes, because of their unique carbophilic nature, have evolved as efficient catalysts for catalyzing various functionalization reactions of C-C multiple bonds. However, the realization of enantioselective transformations via gold catalysis remains challenging due to the geometrical constraints and coordination behaviors of gold complexes. In this context, merged gold/organocatalysis has emerged as one of the intriguing strategies to achieve enantioselective transformations which could not be possible by using a single catalytic system. Historically, in 2009, this field started with the merging of gold with axially chiral Brønsted acids and chiral amines to achieve enantioselective transformations. Since then, based on the unique reactivity profiles offered by each catalyst, several reports utilizing gold in conjunction with various chiral organocatalysts such as amines, Brønsted acids, N-heterocyclic carbenes, hydrogen-bonding and phosphine catalysts have been documented in the literature. This article demonstrates an up-to-date development in this field, especially focusing on the mechanistic interplay of gold catalysts with chiral organocatalysts.

Silver(I)/Dirhodium(II) Catalytic Platform for Asymmetric N-H Insertion Reaction of Heteroaromatics

Transition-metal-catalyzed enantioselective N-H insertion reactions of carbene species offer a powerful and straightforward strategy to produce chiral nitrogen-containing compounds. Developing highly selective insertion reactions using indole variants can meet synthetic demand. Herein we present an asymmetric insertion reaction into N-H bonds of the aromatic heterocycles using donor/acceptor-substituted diazo compounds based on a heteronuclear catalytic platform. Although a previously developed catalysis comprising chiral silver catalyst or dirhodium(II,II) paddlewheel complexes with and without chiral phosphoric acid showed modest performance, a unique combination of widely available Rh2(OAc)4 and silver(I) phosphate dimer [(S)-TRIP-Ag]2 enabled asymmetric carbene insertion reactions (up to 98% ee). Moreover, the Ag/Rh catalytic system facilitated regioselective and enantioselective C-H functionalization of protic indoles. Mechanistic investigation based on density functional theory indicated that an in situ-generated Ag-Rh trimetallic enolate is protonated in a chiral environment.

Scaffold Editing of Cubanes into Homocubanes, Homocuneanes via Cuneanes

The selective synthesis of cage-type hydrocarbons through the editing of the highly symmetric molecule cubane can be anticipated as one of the efficient approaches. In this paper, we identify a catalyst that facilitates the efficient scaffold isomerization of cubanes into homocubanes. This approach, which involves the direct synthesis of homocubanol esters, is promising as a novel method for the synthesis of phenoxy bioisosteres. Additionally, we observed that the isomerization of 1,4-bis(acyloxymethl)cubane results in the generation of both D2 - and C2 -symmetrical bishomocubanes. The same catalyst was also applied to the isomerization of acyloxymethylcuneanes, producing homocuneanol esters.

Nickel-Catalyzed Asymmetric Synthesis of P-Stereogenic Phosphanyl Hydrazine Building Blocks

Catalytic asymmetric methods for the synthesis of synthetically versatile P-stereogenic building blocks offer an efficient and practical approach for the diversity-oriented preparation of P-chiral phosphorus compounds. Herein, we report the first nickel-catalyzed synthesis of P-stereogenic secondary aminophosphine-boranes by the asymmetric addition of primary phosphines to azo compounds. We further demonstrate that the P-H and P-N bonds on these phosphanyl hydrazine building blocks can be reacted sequentially and stereospecifically to access various P-stereogenic compounds with structural diversity.

Experimental and Theoretical Investigation of Ion Pairing in Gold(III) Catalysts

The ion pairing structure of the possible species present in solution during the gold(III)-catalyzed hydration of alkynes: [(ppy)Au(NHC)Y]X2 and [(ppy)Au(NHC)X]X [ppy = 2-phenylpyridine, NHC = NHCiPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; NHC = NHCmes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene X = Cl-, BF4-, OTf-; Y = H2O and 3-hexyne] are determined. The nuclear overhauser effect nuclear magnetic resonance (NMR) experimental measurements integrated with a theoretical description of the system (full optimization of different ion pairs and calculation of the Coulomb potential surface) indicate that the preferential position of the counterion is tunable through the choice of the ancillary ligands (NHCiPr, NHCmes, ppy, and Y) in [(ppy)Au(NHC)(3-hexyne)]X2 activated complexes that undergo nucleophilic attack. The counterion can approach near NHC, pyridine ring of ppy, and gold atom. From these positions, the anion can act as a template, holding water in the right position for the outer-sphere attack, as observed in gold(I) catalysts.

Hydrogen-Bonded Matched Ion Pair Gold(I) Catalysis

The enantioselective reaction of 1,6-enynes with O-, N-, and C-nucleophiles has been developed by matched ion pair gold(I) catalysis in which the chiral gold(I) cation and anion are H-bonded through a urea group. Very high levels of enantiocontrol are achieved (up to >99:1 er) for a broad scope of substrates. DFT studies demonstrate the importance of the H-bond donor group in anchoring the matched chiral cation- and anion-favoring additional noncovalent interactions.

Highly Enantioselective Radical Cation [2 + 2] and [4 + 2] Cycloadditions by Chiral Iron(III) Photoredox Catalysis

Radical cations show a unique reactivity that is fundamentally different from that of conventional cations and have thus attracted considerable attention as alternative cationic intermediates for novel types of organic reactions. However, asymmetric catalysis to promote enantioselective radical cation reactions remains a major challenge in contemporary organic synthesis. Here, we report that the judicious design of an ion pair consisting of a radical cation and a chiral counteranion induces an excellent level of enantioselectivity. This strategy was applied to enantio-, diastereo-, and regioselective [2 + 2] cycloadditions, as well as enantio-, diastereo-, and regioselective [4 + 2] cycloadditions, by using chiral iron(III) photoredox catalysis. We anticipate that this strategy has the potential to expand the use of several mature chiral anions to develop numerous unprecedented enantioselective radical cation reactions.

Gold-based enantioselective bimetallic catalysis

Multimetallic catalysis is a powerful strategy to access complex molecular scaffolds efficiently from easily available starting materials. Numerous reports in the literature have demonstrated the effectiveness of this approach, particularly for capitalizing on enantioselective transformations. Interestingly, gold joined the race of transition metals very late making its use in multimetallic catalysis unthinkable. Recent literature revealed that there is an urgent need to develop gold-based multicatalytic systems based on the combination of gold with other metals for enabling enantioselective transformations that are not possible to capitalize with the use of a single catalyst alone. This review article highlights the progress made in the field of enantioselective gold-based bimetallic catalysis highlighting the power of multicatalysis for accessing new reactivities and selectivities which are beyond the reach of individual catalysts.

Asymmetric Reactions of N-Phosphonyl/Phosphoryl Imines

The asymmetric reactions of imines continued to attract the attention of the scientific community for decades. However, the stereoselective reactions of N-phosphonyl/phosphoryl imines remained less explored as compared to other N-substituted imines. The chiral auxiliary-based asymmetric-induction strategy with N-phosphonyl imines could effectively generate enantio- and diastereomeric amine, α,β-diamine, and other products through various reactions. On the other hand, the asymmetric approach for the generation of chirality through the utilization of optically active ligands, along with metal catalysts, could be successfully implemented on N-phosphonyl/phosphoryl imines to access numerous synthetically challenging chiral amine scaffolds. The current review critically summarizes and reveals the literature precedence of more than a decade to highlight the major achievements existing to date that can display a clear picture of advancement as well drawbacks in this area.

Enantioselective transition-metal catalysis via an anion-binding approach

Asymmetric transition-metal catalysis represents a powerful strategy for accessing enantiomerically enriched molecules1-3. The classical strategy for inducing enantioselectivity with transition-metal catalysts relies on direct complexation of chiral ligands to produce a sterically constrained reactive metal site that allows formation of the major product enantiomer while effectively inhibiting the pathway to the minor enantiomer through steric repulsion4. The chiral-ligand strategy has proven applicable to a wide variety of highly enantioselective transition-metal-catalysed reactions, but important scenarios exist that impose limits to its successful adaptation. Here, we report a new approach for inducing enantioselectivity in transition-metal-catalysed reactions that relies on neutral hydrogen-bond donors (HBDs)5,6 that bind anions of cationic transition-metal complexes to achieve enantiocontrol and rate enhancement through ion pairing together with other non-covalent interactions7-9. A cooperative anion-binding effect of a chiral bis-thiourea HBD is demonstrated to lead to high enantioselectivity (up to 99% enantiomeric excess) in intramolecular ruthenium-catalysed propargylic substitution reactions10. Experimental and computational mechanistic studies show the attractive interactions between electron-deficient arene components of the HBD and the metal complex that underlie enantioinduction and the acceleration effect.

Enantioselective Hydroalkoxylation of 1,3-Dienes via Ni-Catalysis

As an advance in hydrofunctionalization, we herein report that alcohols add to 1,3-dienes with high regio- and enantioselectivity. Using Ni-DuPhos, we access enantioenriched allylic ethers. Through the choice of solvent-free conditions, we control the reversibility of C-O bond formation. This work showcases a rare example of methanol as a reagent in asymmetric synthesis.

Silver-Catalyzed Direct Nucleophilic Cyclization: Enantioselective De Novo Synthesis of C-C Axially Chiral 2-Arylindoles

Atropisomeric indoles widely exist in natural products, pharmaceuticals, functional materials, and catalysts for their featured biological activities, photoelectric properties, and catalytic activities, while facile and de novo construction of this motif remains underexplored. Herein, we report a chiral silver phosphate-catalyzed direct 5-endo-dig nucleophilic cyclization of 2-alkynylanilins under mild conditions, affording various C-C axially chiral 2-arylindoles in high to excellent yields and enantioselectivities. Control experiments implied the cooperative catalysis of AgOAc and chiral phosphoric acid, wherein the former accelerated the desired transformation while the latter improved the enantioselectivity. In addition, as the first example of silver-catalyzed enantioselective de novo synthesis of C-C axially chiral indole skeletons, synthetic applications and products' thermal stability have been investigated.

Chiral BINOL-based borate counterions: from cautionary tale on anion stability to enantioselective Cu-catalyzed cyclopropanation

The chiral weakly coordinating (3,3'-biphenyl-BINOL)BF₂ anion can be generated by the reaction of the BINOL derivative with Cu(NCMe)₄BF₄. Structural analysis suggest the anion is weakly coordinating to Cu⁺. However, its use in cyclopropanation reactions leads to the rearrangement of the anion to create a chiral 3,3'-diphenyl-BINOL ligand that coordinates to copper. The latter suggests an important feature to consider when using weakly association anions, but can also be used to design simple chiral BINOL-based ligands for asymmetric cyclopropanation.

H-Bonded Counterion-Directed Catalysis: Enantioselective Gold(I)-Catalyzed Addition to 2-Alkynyl Enones as a Case Study

H-bonded counterion-directed catalysis (HCDC) is a strategy wherein a chiral anion that is hydrogen-bonded to the achiral ligand of a metal complex is responsible for enantioinduction. In this article we present the application of H-bonded counterion-directed catalysis to the Au(I)-catalyzed enantioselective tandem cycloisomerization-addition reaction of 2-alkynyl enones. Following the addition of C-, N- or O-centered nucleophiles, bicyclic furans were obtained in moderate to excellent yield and enantioselectivity (28 examples, 59-96 % yield, 62 : 38 to 95 : 5 er). The optimal catalytic system, comprising a phosphinosquaramide Au(I) chloride complex and a BINOL-derived phosphoramidate Ag(I) salt, was selected in a combinatorial fashion from a larger library with the help of high-throughput screening. An enantioselectivity switch of ca. 120 Δee% was observed upon addition of the achiral Au(I) component to the Ag(I) salt.

Strategies That Utilize Ion Pairing Interactions to Exert Selectivity Control in the Functionalization of C-H Bonds

Electrostatic attraction between two groups of opposite charge, typically known as ion-pairing, offers unique opportunities for the design of systems to enable selectivity control in chemical reactions. Catalysis using noncovalent interactions is an established and vibrant research area, but it is noticeable that hydrogen bonding interactions are still the main interaction of choice in system design. Opposite charges experience the powerful force of Coulombic attraction and have the ability to exert fundamental influence on the outcome of reactions that involve charged reagents, intermediates or catalysts. In this Perspective, we will examine how ion-pairing interactions have been used to control selectivity in C-H bond functionalization processes. This broad class of reactions provides an interesting and thought-provoking lens through which to examine the application of ion-pairing design strategies because it is one that encompasses great mechanistic diversity, poses significant selectivity challenges, and perhaps most importantly is of immense interest to synthetic chemists in both industry and academia. We survey reactions that proceed via radical and ionic mechanisms alongside those that involve transition metal catalysis and will deal with control of site-selectivity and enantioselectivity. We anticipate that as this emerging area develops, it will become an ever-more important design strategy for selectivity control.

Understanding the Regioselectivity of Ion-Pair-Assisted Meta-Selective C(sp2)-H Activation in Conformationally Flexible Arylammonium Salts

The lack of directionality and the long-range nature of Coulomb interactions have been a bottleneck to achieve chemically precise C-H activation using ion-pairs. Recent report by Phipps and co-workers of the ion-pair-directed regioselective Iridium-catalyzed borylation opens a new direction toward harnessing noncovalent interactions for C-H activation. In this article, the mechanism and specific role of ion-pairing are investigated using density functional theory (DFT). Computational studies reveal that meta C-H activation is kinetically more favorable than the para analogue due to stronger electrostatic interactions between the ion-pairs in closer proximity [d(NMe₃⁺···SO₃^-)_TSP1m = 3.93 Å versus d(NMe₃⁺···SO₃^-)_TSP1p = 4.30 Å]. The electrostatic interactions overwhelm the Pauli repulsion and distortion interactions incurred in bringing the oppositely charged ions in close contact for the rate-limiting meta transition state (TSP1_m). Multiple linear regression shows that the free energies of activation correlate well with descriptors like the charge densities on the meta carbon and Ir atom along with that on the cation and anion with R² = 0.74. Tuned range-separated DFT calculations demonstrate accurately the localization of charge separation in the reactant complex and transition state for the meta selectivity.

Theoretical study on the mechanism, chemo- and enantioselectivity of the Ag- vs. Rh-catalyzed intramolecular carbene transfer reaction of diazoacetamides

To explore the mechanism of silver and rhodium catalysis and reveal the origin of the chemo- and enantioselectivity of the reaction, density functional theory calculations were performed on the first silver-catalyzed highly enantioselective carbene transfer reaction. The calculation results reveal that when silver is used as a catalyst, due to the participation of the phosphate anion in the transition state, the enhanced nucleophilicity of the α-diazoacetamide unit promotes smooth dearomatization before generation of the silver carbene. Because the generated rhodium carbene has stronger electrophilicity, typical carbene reactions (C-H insertion and the Büchner reaction) are favored. In addition, in the process of silver catalyzed dearomatization, the formation of an R-type transition state is determined by the small torsion energy and strong interaction energy.

Chirality in Organic and Mineral Systems: A Review of Reactivity and Alteration Processes Relevant to Prebiotic Chemistry and Life Detection Missions

Chirality is a central feature in the evolution of biological systems, but the reason for biology’s strong preference for specific chiralities of amino acids, sugars, and other molecules remains a controversial and unanswered question in origins of life research. Biological polymers tend toward homochiral systems, which favor the incorporation of a single enantiomer (molecules with a specific chiral configuration) over the other. There have been numerous investigations into the processes that preferentially enrich one enantiomer to understand the evolution of an early, racemic, prebiotic organic world. Chirality can also be a property of minerals; their interaction with chiral organics is important for assessing how post-depositional alteration processes could affect the stereochemical configuration of simple and complex organic molecules. In this paper, we review the properties of organic compounds and minerals as well as the physical, chemical, and geological processes that affect organic and mineral chirality during the preservation and detection of organic compounds. We provide perspectives and discussions on the reactions and analytical techniques that can be performed in the laboratory, and comment on the state of knowledge of flight-capable technologies in current and future planetary missions, with a focus on organics analysis and life detection.

A Chiral Iron Disulfonate Catalyst for the Enantioselective Synthesis of 2-Amino-2'-hydroxy-1,1'-binaphthyls (NOBINs)

A novel type of chiral redox disulfonate iron complex for asymmetric catalysis is reported. The [Fe((R_a)-BINSate)]⁺ (BINSate = 1,1'-binaphthalene-2,2'-disulfonate) complex effectively promotes the enantioselective oxidative cross-coupling between 2-naphthols (1) and 2-aminonaphthalene derivatives (2), affording optically enriched (R_a)-2-amino-2'-hydroxy-1,1'-binaphthyls (NOBINs) with exceptional yields and enantioselective ratios (up to 99% yield and 96:4 er). The [Fe((R_a)-BINSate)]⁺ catalyst was designed as a chiral version of FeCl₃ with multicoordination sites available for binding the two coupling partners 1 and 2 as well as the oxidant. Our structure-selectivity and activity study, which covered most of the important positions in the NOBIN scaffold, revealed the effect of different substitution patterns on the coupling efficiency and stereoselectivity.

H-Bonded Counterion-Directed Enantioselective Au(I) Catalysis

A new strategy for enantioselective transition-metal catalysis is presented, wherein a H-bond donor placed on the ligand of a cationic complex allows precise positioning of the chiral counteranion responsible for asymmetric induction. The successful implementation of this paradigm is demonstrated in 5-exo-dig and 6-endo-dig cyclizations of 1,6-enynes, combining an achiral phosphinourea Au(I) chloride complex with a BINOL-derived phosphoramidate Ag(I) salt and thus allowing the first general use of chiral anions in Au(I)-catalyzed reactions of challenging alkyne substrates. Experiments with modified complexes and anions, ¹H NMR titrations, kinetic data, and studies of solvent and nonlinear effects substantiate the key H-bonding interaction at the heart of the catalytic system. This conceptually novel approach, which lies at the intersection of metal catalysis, H-bond organocatalysis, and asymmetric counterion-directed catalysis, provides a blueprint for the development of supramolecularly assembled chiral ligands for metal complexes.

Convenient synthesis of tricyclic N(1)-C(2)-fused oxazino-indolones via [Au(I)] catalyzed hydrocarboxylation of allenes

A new [Au(I)] catalyzed intramolecular hydrocarboxylation of allenes is presented as a valuable synthetic route to oxazino-indolones. The employment of 3,5-(CF3)2-C6H3-ImPyAuSbF6 as the optimal catalyst (5 mol%) was necessary to...

Medium and Large N-Heterocycle Formation via Allene Hydroamination with a Bimetallic Rh(II) Catalyst

We report the synthesis of a 2-phosphinoimidazole-derived bimetallic Rh(II) complex that enables intramolecular allene hydroamination to form 7- to 10-member rings in high yield. Monometallic Rh complexes, in contrast, fail to achieve any product formation. We demonstrate a broad substrate scope for formation of various N-heterocycles. Macrocyclizations that form 11- to 15-member N-heterocycles are also demonstrated. Mechanistic studies suggest that the reaction proceeds via reversible allene insertion with a Rh-hydride followed by C-N bond-forming reductive elimination. We hypothesize that the reactivity observed with our catalyst vs monometallic Rh complexes is derived from the bimetallic nature of our complex.

Catalytic Asymmetric Hydroalkoxylation of C-C Multiple Bonds

Asymmetric hydroalkoxylation of alkenes constitutes a redox-neutral and 100% atom-economical strategy toward enantioenriched oxygenated building blocks from readily available starting materials. Despite their great potential, catalytic enantioselective additions of alcohols across a C-C multiple bond are particularly underdeveloped, especially compared to other hydrofunctionalization methods such as hydroamination. However, driven by some recent innovations, e.g., asymmetric MHAT methods, asymmetric photocatalytic methods, and the development of extremely strong chiral Brønsted acids, there has been a gratifying surge of reports in this burgeoning field. The goal of this review is to survey the growing landscape of asymmetric hydroalkoxylation by highlighting exciting new advances, deconstructing mechanistic underpinnings, and drawing insight from related asymmetric hydroacyloxylation and hydration. A deep appreciation of the underlying principles informs an understanding of the various selectivity parameters and activation modes in the realm of asymmetric alkene hydrofunctionalization while simultaneously evoking the outstanding challenges to the field moving forward. Overall, we aim to lay a foundation for cross-fertilization among various catalytic fields and spur further innovation in asymmetric hydroalkoxylations of C-C multiple bonds.