Palladium-Catalyzed Nucleophilic Reaction of Alkylidenecyclopropanes with β,γ-Unsaturated α-Ketoesters: Ligand-Controlled Divergent Synthesis

A palladium-catalyzed ligand-controlled selective 1,4-addition and cycloaddition reaction of β,γ-unsaturated α-ketoesters with alkylidenecyclopropanes (ACPs) has been developed. Using ACPs and β,γ-unsaturated α-ketoesters as starting materials, γ-dienyl-α-ketoesters and dihydro-2H-pyrans could be prepared selectively by modulating the ligand. A range of multisubstituted α-ketoesters and dihydro-2H-pyrans were obtained in moderate to excellent yields with excellent regioselectivities.

Cobalt-catalyzed branched selective hydroallylation of terminal alkynes

Here, we reported a cobalt-hydride-catalyzed Markovnikov-type hydroallylation of terminal alkynes with allylic electrophile to access valuable and branched skipped dienes (1,4-dienes) with good regioselectivity. This operationally simple protocol exhibits excellent functional group tolerance and exceptional substrate scope. The reactions could be carried out in gram-scale with TON (turn over number) up to 1160, and the products could be easily derivatized. The preliminary mechanism of electrophilic allylation of α-selective cobalt alkenyl intermediate was proposed based on deuterium labeling experiment and kinetic studies.

Selectively generating “skipped” dienes, where two carbon–carbon double bonds are separated by a saturated carbon center, is an interesting problem in organic chemistry, with few reliable, catalytic methods currently available. Here, the authors report branched selective hydroallylation of terminal alkynes with allylic bromides to form skipped dienes, via cobalt catalysis.

Ligand-Controlled Cobalt-Catalyzed Regiodivergent Alkyne Hydroalkylation

Regiodivergent alkyne hydroalkylation to generate different isomers of an alkene from the same alkyne starting material would be beneficial; however, it remains a challenge. Herein, we report a ligand-controlled cobalt-catalyzed regiodivergent alkyne hydroalkylation. The sensible selection of bisoxazoline (L1) and pyridine-oxazoline (L8) ligands led to reliable and predictable protocols that provided (E)-1,2-disubstituted and 1,1-disubstituted alkenes with high E/Z stereoselectivity and regioisomeric ratio starting from identical terminal alkyne and alkyl halide substrates and produced trisubstituted alkenes in the case of internal alkynes. This method exhibits a broad scope for terminal and internal alkynes with a wide range of activated and unactivated alkyl halides and shows excellent functional group compatibility.

Orthogonal Access to α-/β-Branched/Linear Aliphatic Amines by Catalyst-Tuned Regiodivergent Hydroalkylations

Linear, α-branched, and β-branched aliphatic amines are widespread in pharmaceuticals, agrochemicals, and fine chemicals. Thus, the development of direct and efficient methods to these structures in a tunable manner is highly desirable yet challenging. Herein, a catalyst-controlled synthesis of α-branched, β-branched and linear aliphatic amines from Ni/Co-catalyzed regio- and site-selective hydroalkylations of alkenyl amines with alkyl halides is developed. This catalytic protocol features the reliable prediction and control of the coupling position of alkylation to provide orthogonal access to α-branched, β-branched and linear alkyl amines from identical starting materials. This platform unlocks orthogonal reactivity and selectivity of nickel hydride and cobalt hydride chemistry to catalytically repurpose three types of alkyl amines under mild conditions.

Ni-Catalyzed Divergent Synthesis of 2-Benzazepine Derivatives via Tunable Cyclization and 1,4-Acyl Transfer Triggered by Amide N-C Bond Cleavage

Ligand-directed divergent synthesis can transform common starting materials into distinct molecular scaffolds by simple tuning different ligands. This strategy enables the rapid construction of structurally rich collection of small molecules for biological evaluation and reveals novel modes of catalytic transformation, representing one of the most sought-after challenges in synthetic chemistry. We herein report a Ni-catalyzed ligand-controlled tunable cyclization/cross-couplings for the divergent synthesis of pharmacologically important 2-benzazepine frameworks. The bidentate ligand facilitates the nucleophilic addition of the aryl halides to the amide carbonyl, followed by 1,4-acyl transfer and cross-coupling to obtain 2-benzazepin-5-ones and benzo[c]pyrano[2,3-e]azepines. The tridentate ligand promotes the selective 7-endo cyclization/cross-coupling to access to 2-benzazepin-3-ones. The protocol operates under mild reaction conditions with divergent cyclization patterns that can be easily modulated through the ligand backbone.

Regiodivergent C-N Coupling of Quinazolinones Controlled by the Dipole Moments of Tautomers

Herein, we report that the dipole moments of tautomers can be the controlling factor for regiodivergent synthesis of either 14H-quinazolino[3,2-f]phenanthridin-14-ones or 6H-quinazolino[1,2-f]phenanthridin-6-ones, selectively, from unmasked 2-([1,1'-biphenyl]-2-yl)quinazolin-4(3H)-one. An intramolecular C(sp²)-NH coupling reaction mediated by PhI(OCOOCF₃)₂ could lead to two different regioisomers selectively at different temperatures when the dielectric constants of solvents like hexafluoroisopropanol and trifluoroacetic acid matched with the tautomer's dipole moments.

Catalyst-controlled selective borocarbonylation of benzylidenecyclopropanes: regiodivergent synthesis of γ-vinylboryl ketones and β-cyclopropylboryl ketones

Regioselective catalytic multi-functionalization reactions enable the rapid synthesis of complexed products from the same precursors. In this communication, we present a method for the regiodivergent borocarbonylation of benzylidenecyclopropanes with aryl iodides. Various γ-vinylboryl ketones and β-cyclopropylboryl ketones were produced in moderate to good yields with excellent regioselectivity from the same substrates. The choice of the catalyst is key for the regioselectivity control: γ-vinylboryl ketones were produced selectively with IPrCuCl and Pd(dppp)Cl₂ as the catalytic system, while the corresponding β-cyclopropylboryl ketones were obtained in high regioselectivity with Cu(dppp)Cl, [Pd(η³-cinnamyl)Cl]₂ and xantphos as the catalytic system. Moreover, γ-vinylboryl ketones and β-cyclopropylboryl ketones were successfully transformed into several other value-added products.

A novel procedure for regiodivergent borocarbonylation of benzylidenecyclopropanes has been developed. A variety of valuable γ-vinylboryl ketones and β-cyclopropylboryl ketones can be obtained selectively in excellent yields.

Solvent- and Metal-Controlled Regiodivergent Synthesis of Tri­fluoromethylated Pyrazol-3-yl- and Pyrazol-5-ylphosphonates

Convenient approaches to the selective syntheses of trifluoro­methylated pyrazol-3-yl- and pyrazol-5-ylphosphonates have been developed based on solvent- and metal-controlled reaction of diethyl (4,4,4-trifluoro-3-oxobut-1-yn-1-yl)phosphonate and monosubstituted hydrazines.

Aluminium complexes: next-generation catalysts for selective hydroboration

Organoboranes obtained from hydroboration reactions are one of the important classes of compounds that could be used to provide valuable synthons for follow-up transformations such as various functional group incorporation or C-C bond forming reactions. For decades, various transition metals were utilised as catalysts in such transformations. Recently Earth-abundant and less toxic main group metals have revived their importance in hydroboration chemistry, among which the suitable candidates are aluminium complexes as catalysts. In this regard, the development of aluminium complexes to achieve more robust catalytic systems with greater efficiency is appreciable.

A covalent modification strategy for di-alkyne tagged metal–organic frameworks to access efficient heterogeneous catalysts toward C–C bond formation

A di-alkyne tagged MOF was proposed to introduce diverse metals, and UiO-66-(alkyne-Co)2 displayed an efficient catalytic performance for the Knoevenagel reaction.

Direct α-methylenation of triazines to terminal olefins with DMA

We report an efficient metal (Cu or Ni)-catalysed α-methylenation of triazines to terminal olefins using DMA as a one-carbon source. Various substituted triazine derivatives are suitable for this reaction.

Transition-Metal-Catalyzed Divergent C-H Functionalization of Five-Membered Heteroarenes

Conversion of common reactants to diverse products is a key objective of organic syntheses. Recent developments in transition-metal-catalyzed C-H functionalization have increased the interest in such conversions. Both the position of functionalization and the type of the substituent can be varied, allowing systematic diversification of common structural cores. Because five-membered heteroarenes (pyrazole, imidazole, thiazole, pyrrole, and thiophene) are ubiquitous in pharmaceuticals and organic functional materials, the selective C-H functionalization of these heterocyclic cores facilitates both the optimization of their physicochemical properties and streamlining of their preparation. In addition, the parent forms of these heterocycles are more readily available and inexpensive than any other derivatives of their families. Hence, their nondirected C-H functionalization is highly desirable. Although various regioselective reactions have been developed, many of them target the most reactive site; hence, except for some extensively studied arylation reactions, regiodivergent functionalization of two or more sites has been limited.This Account summarizes our work on the regiodivergent, nondirected C-H functionalization of five-membered heteroarenes with alkenes and alkynes. These unsaturated hydrocarbons are readily available, and all the composing atoms can be incorporated into products with high atom efficiency. Furthermore, the installed alkenyl groups can be transformed to other useful functional groups. To achieve comparable selectivity to that observed in the traditional reactions of these heteroarenes with highly electrophilic reagents and strong bases, a transition metal catalytic system was carefully devised with a more streamlined synthesis. A judicious choice of metals, ligands, acid and base additives, and solvents orchestrates divergent transformations using electronic and steric effects of the heteroarenes. Although C-H cleavage is a rate- and site-selectivity-determining step in most cases, the subsequent steps involving the formation of C-C bonds are often more critical than the other steps. For the C-H cleavage step, modulating the electronic properties of catalysts to make them electrophilic allows preferential alkenylation at the nucleophilic position. In addition, the presence of an internal base that can be exploited for concerted metalation-deprotonation of the acidic C-H bond offers alternative regioselectivity. Furthermore, we developed our own ligand system based on a conformationally rigid pyrazolonaphthyridine scaffold that enables aerobic C-H alkenylation reactions with steric control. We showed that the electronic and steric effects of heteroarenes can be further extended to chemodivergent reactions with norbornene derivatives. Depending on whether the palladacycle is formed, heteroarenes selectively undergo 1:2 annulation with norbornene derivatives and three-component reactions with other azoles through the Pd-norbornene adducts or Catellani and 2:1 annulation reactions through the palladacycle intermediates.Other research groups have also contributed to the development of divergent reactions, in investigations ranging from the pioneering studies in the early days of research on C-H functionalization to recent studies with new ligands. We have also discussed these studies in context. These approaches provide access to many heteroarenes with systematically varied substituents. We believe that new ligand systems and mechanistic insights gained through these studies will enrich fields beyond C-H functionalization of five-membered heteroarenes.

Direct access to tetrasubstituted cyclopentenyl scaffolds through a diastereoselective isocyanide-based multicomponent reaction

An efficient strategy combining the stereocontrol of organocatalysis with the diversity-generating character of multicomponent reactions is described to produce structurally unique, tetrasubstituted cyclopentenyl frameworks. An asymmetric Michael addition-hemiacetalization between α-cyanoketones and α,β-unsaturated aliphatic aldehydes was performed for constructing cyclic hemiacetals, which were next employed as chiral bifunctional substrates in a new diastereoselective intramolecular isocyanide-based multicomponent reaction. This approach furnished a diversity of structurally complex compounds - including peptidomimetics and natural product hybrids in high stereoselectivity (up to >99% ee and up to >99 : 1 dr) and in moderate to high yields.

Directing-group-free catalytic dicarbofunctionalization of unactivated alkenes

In the absence of directing auxiliaries, the catalytic addition of carbogenic groups to unactivated alkenes with control of regioselectivity remains an ongoing challenge in organic chemistry. Here we describe a directing-group-free, nickel-catalysed strategy that couples a broad array of unactivated and activated olefins with aryl-substituted triflates and organometallic nucleophiles to afford diarylation adducts in either regioisomeric form, in up to 93% yield and >98% site selectivity. By switching the reagents involved, the present strategy may be extended to other classes of dicarbofunctionalization reactions. Mechanistic and computational investigations offer insights into the origin of the observed regiochemical outcome and the utility of the method is highlighted through the concise syntheses of biologically active molecules. The catalyst control principles reported are expected to advance efforts towards the development of general site-selective alkene functionalizations, removing the requirement for neighbouring activating groups.

Ligand-controlled regioselective and chemodivergent defluorinative functionalization of gem-difluorocyclopropanes with simple ketones

Modulating the reaction selectivity is highly attractive and pivotal to the rational design of synthetic regimes. The defluorinative functionalization of gem-difluorocyclopropanes constitutes a promising route to construct β-vinyl fluorine scaffolds, whereas chemo- and regioselective access to α-substitution patterns remains a formidable challenge. Presented herein is a robust Pd/NHC ligand synergistic strategy that could enable the C-F bond functionalization with exclusive α-regioselectivity with simple ketones. The key design adopted enolates as π-conjugated ambident nucleophiles that undergo inner-sphere 3,3'-reductive elimination warranted by the sterically hindered-yet-flexible Pd-PEPPSI complex. The excellent branched mono-defluorinative alkylation was achieved with a sterically highly demanding IHept ligand, while subtly less bulky SIPr acted as a bifunctional ligand that not only facilitated α-selective C(sp3)-F cleavage, but also rendered the newly-formed C(sp2)-F bond as the linchpin for subsequent C-O bond formation. These examples represented an unprecedented ligand-controlled regioselective and chemodivergent approach to various mono-fluorinated terminal alkenes and/or furans from the same readily available starting materials.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Regiodivergent CDC reactions of aromatic aldehydes with unactivated arenes controlled by transient directing strategy

The regiodivergent catalytic dehydrogenative cross-coupling reactions at both sp² and sp³ hybridized carbons of aromatic compounds are particularly challenging. Herein, we report the finding of transient directing group controlled regiodivergent C(sp³)-C(sp²) and C(sp²)-C(sp²) cross-coupling in the o-methyl benzaldehyde frameworks. Catalyzed by palladium, using K₂S₂O₈ or [F⁺] reagents as by-standing oxidants and unactivated arenes as substrates/solvents, various benzyl benzaldehydes or phenyl benzaldehydes were prepared. A mechanism study indicated that the regiospecificity is dominated by the [5,6]-fused palladacycle or [6,5]-fused palladacycle intermediates, which are generated from Pd-chelation with specified transient directing groups and further C-H activations.

Ligand-Controlled Regiodivergence for Catalytic Stereoselective Semireduction of Allenamides

Ligand-controlled regiodivergence has been developed for catalytic semireduction of allenamides with excellent chemo- and stereocontrol. This system also provides an example of catalytic regiodivergent semireduction of allenes for the first time. The divergence of the semireduction is enabled by ligand switch with the same palladium pre-catalyst under operationally simple and mild conditions. Monodentate ligand XPhos exclusively promotes selective 1,2-semireduction to afford allylic amides, while bidentate ligand BINAP completely switched the regioselectivity to 2,3-semireduction, producing (E)-enamide derivatives.

Ligand-Regulated Palladium-Catalyzed Regiodivergent Hydroarylation of the Distal Double Bond of Allenamides with Aryl Boronic Acid

The ligand-regulated regiodivergent hydroarylation of the distal double bond of allenamides with aryl boronic acid was achieved in the presence of palladium(II) catalysts, delivering a variety of functionalized enamide with excellent E selectivity and Markovnikov/anti-Markovnikov selectivity. Two possible coordination intermediates were proposed to be responsible for the regiodivergent hydroarylation: (1) The coordination Intermediate I, which was proposed to be formed through the coordination of MeCN, distal double bond, phenyl to palladium, led to the aryl group away from the Intermediate I, inducing excellent E selectivity and anti-Markovnikov selectivity. (2) A switch of regioselectivity to 1,2-Markovnikov hydroarylation was obtained using bidentate phosphine ligand (dppf or Xantphos). The formed coordination Intermediate II led to the N-tether away from the Intermediate II and at the trans position of aryl, resulting in excellent E selectivity and Markovnikov selectivity. Meanwhile, tentative investigation on the mechanism proved that the hydron source of this hydroarylation is more likely to be boronic acid. The transmetallation between aryl boronic acid and palladium catalyst was the initial step of this transformation.

In vivo organic synthesis by metal catalysts

The metal-catalyzed reactions have given various chemical modifications that could not be achieved through basic organic chemistry reactions. In the past decade, many metal-mediated catalytic systems have carried out different transformations in cellulo, such as decaging of fluorophores, drug release, and protein conjugation. However, translating abiotic metal catalysts for organic synthesis in vivo, including bacteria, zebrafish, or mice, could encounter numerous challenges regarding their biocompatibility, stability, and reactivity in the complicated biological environment. In this review, we categorize and summarize the relevant advances in this research field by emphasizing the system's framework, the design of each transformation, and the mode of action. These studies disclose the massive potential of the emerging field and the significant applications in synthetic biology.

Generation of zwitterionic trifluoromethyl N-allylic ylides and their use in switchable divergent annulations

The previously unreported zwitterionic N-allylic ylide species from the corresponding Morita-Baylis-Hillman carbonates of trifluoromethyl ketones and acrylonitrile are generated under the catalysis of cinchona-derived tertiary amines, and subsequently participate in switchable asymmetric [3+2] or [4+1] annulations with 1-azadienes in chemo-, regio-, and stereodivergent manners via catalyst or substrate control. A diverse range of frameworks, having a trifluoromethylated all-carbon quaternary stereogenic centre or a tetrasubstituted alkene moiety, are generally constructed in good yields with excellent enantioselectivity.