Kinetically Controllable Pd-Catalyzed Decarboxylation Enabled [5 + 2] and [3 + 2] Cycloaddition toward Carbocycles Featuring Quaternary Carbons

Merging of Palladium and Organocatalysis Enabled Asymmetric Decarboxylative (2+1) Cycloadditions toward Cyclopropanes

A cascade reaction enabling enantio- and diastereoselective construction of strained cyclopropanes is described. This asymmetric (2+1) annulation process uses vinyl methylene carbonate and 2-cyanoacrylate as reaction partners in the presence of Pd(PPh3)4 as a precatalyst and an enantioenriched phosphoramidite ligand featuring a morpholine functionality. Mechanistic investigations unveil that the PPh3 derived from the Pd(PPh3)4 and the morpholine-containing phosphoramidite work as cooperative phosphorus and Brønsted base catalysts to promote the reaction.

Palladium-Catalyzed Ligand-Controlled Switchable Hetero-(5 + 3)/Enantioselective [2σ+2σ] Cycloadditions of Bicyclobutanes with Vinyl Oxiranes

For nearly 60 years, significant research efforts have been focused on developing strategies for the cycloaddition of bicyclobutanes (BCBs). However, higher-order cycloaddition and catalytic asymmetric cycloaddition of BCBs have been long-standing formidable challenges. Here, we report Pd-catalyzed ligand-controlled, tunable cycloadditions for the divergent synthesis of bridged bicyclic frameworks. The dppb ligand facilitates the formal (5+3) cycloaddition of BCBs and vinyl oxiranes, yielding valuable eight-membered ethers with bridged bicyclic scaffolds in 100% regioselectivity. The Cy-DPEphos ligand promotes selective hetero-[2σ+2σ] cycloadditions to access pharmacologically important 2-oxabicyclo[3.1.1]heptane (O-BCHeps). Furthermore, the corresponding catalytic asymmetric synthesis of O-BCHeps with 94-99% ee has been achieved using chiral (S)-DTBM-Segphos, representing the first catalytic asymmetric cross-dimerization of two strained rings. The obtained O-BCHeps are promising bioisosteres for ortho-substituted benzenes.

Asymmetric (4+1) Annulations by Cascade Allylation and Transient σ-Alkyl-Pd(II) Initiated Allylic Csp3 -H Activation

A unique Pd-catalyzed approach for asymmetric (4+1) annulations via cascade allylation and transient σ-alkyl-Pd(II) initiated methylene Csp3 -H activation is reported. The enolate fragment derived from the decarboxylation of vinyl methylene carbonate is crucial to stabilize the key intermediate. These reactions enable the synthesis of various useful dihydrobenzofurans with excellent enantioselectivity, typically >95 : 5 er, and exclusive (Z)-stereoselectivity. Compared with the well-established annulations via Heck-type C-H activations, this protocol showcases a conceptually new way to generate σ-alkyl-Pd(II) species that could initiate challenging asymmetric Csp3 -H activations.

Palladium-catalyzed decarboxylative α-allylation of thiazolidinones and azlactones with sulfonamido-substituted acyclic allylic carbonates

A palladium-catalyzed decarboxylative α-allylation of thiazolidinones and azlactones with aza-π-allylpalladium zwitterionic intermediates, in situ generated from sulfonamido-substituted allylic carbonates, is successfully developed. This method allows the formation of a series of structurally diverse 5-alkylated thiazolidinones and 2-piperidones under mild conditions in moderate to high yields (up to 99% yield).

Decarboxylative Intramolecular [3 + 2] Cycloaddition of Cyclic Enol Carbonates: Construction of a Bicyclo[3.3.0]octanone Skeleton

Stereoselective synthesis of bicyclic cyclopentanones was achieved by sequential Tf2O-catalyzed decarboxylation and intramolecular [3 + 2] cycloaddition reactions of cyclic enol carbonates bearing an alkene unit. Four stereogenic centers in the obtained cyclopentanone were stereoselectively constructed. This method could be applied to the synthesis of various fused bicyclic products in moderate-to-good yields.

Palladium-Catalyzed Asymmetric (3 + 2) Cycloaddition of 5-Allenyloxazolidine-2,4-Diones with Barbiturate-Derived Alkenes: Synthesis of Spirobarbiturate-γ-Lactams

The 5-allenyloxazolidine-2,4-diones had been synthesized as novel precursors of π-allyl palladium zwitterion and were applied in a palladium-catalyzed enantioselective (3 + 2) annulation by using barbiturate-derived alkenes as the reaction partner in the presence of an axially chiral phosphoramidite ligand. This reaction proceeded smoothly under mild reaction conditions, affording highly functionalized spirobarbiturate-γ-lactam derivatives in excellent yields along with high diastereo- and enantioselectivities. The scale-up reaction and further transformation of the product were also successful.

Tandem Allylic Amination/oxa-Michael Addition of Vinyl Methylene Cyclic Carbonates via Palladium-Organo Relay Catalysis

A tandem allylic amination/oxa-Michael addition of vinyl methylene cyclic carbonates (VMCCs) has been developed to construct heterocycles by single palladium catalysis or palladium-organo relay catalysis. In this process, the bisnucleophiles first underwent regioselective allylic amination, and then the second nucleophilic group further completed the hetero-Michael addition reaction to form a series of heterocycles. Among them, the chiral 3,4-dihydro-2H-benzo[b][1,4]oxazines could be produced in medium to high yield with good enantioselectivity under a palladium-organo relay catalysis.

Decarboxylative 1,2-rearrangement of cyclic carbonates promoted by Lewis acid

A Lewis acid-mediated decarboxylative 1,2-rearrangement reaction of cyclic carbonates was developed. The selectivity of the migration in the decarboxylative 1,2-rearrangement of cyclic carbonates was opposite to that of the corresponding 1,2-diols under the same reaction conditions. This contrasting selectivity of the migration was confirmed in a variety of substrates.

[3+2] Cycloaddition of alkyl aldehydes and alkynes enabled by photoinduced hydrogen atom transfer

[3+2] Cycloaddition is a step- and atom-economic method for the synthesis of five-membered rings. Despite the great success of 1,3-dipolar cycloadditions, the radical [3+2] annulation of alkynes remains a formidable challenge. Herein, a photoinduced decatungstate-catalyzed [3+2] cycloaddition of various internal alkynes using abundant aliphatic aldehydes as a three-carbon synthon is developed, producing elaborate cyclopentanones in 100% atom economy with excellent site-, regio-, and diastereoselectivity under mild conditions. The catalytic cycle consists of hydrogen atom abstraction from aldehydes, radical addition, 1,5-hydrogen atom transfer, anti-Baldwin 5-endo-trig cyclization, and back hydrogen abstraction. The power of this method is showcased by the late-stage elaboration of medicinally relevant molecules and total or formal synthesis of (±)-β-cuparenone, (±)-laurokamurene B, and (±)-cuparene.

In contrast to the prevalence of 1,3-dipolar cycloadditions, radical [3+2] annulations of alkynes are underexplored. Here, the authors describe [3+2] cycloadditions of various internal alkynes with readily accessible aliphatic aldehydes via photoinduced decatungstate catalysis.

High-order dipolar annulations with metal-containing reactive dipoles

Medium-sized heterocycles are widespread among a spectrum of structurally intriguing and biologically significant natural products and synthetic pharmaceuticals. Metal-catalyzed high-order dipolar annulations resembling reactions of metal-containing reactive dipoles with dipolarophiles constitute a highly efficient and flexible strategy for constructing medium-sized heterocycles. Mechanistically, these annulation reactions usually proceeding through stepwise pathways are different from the classic high-order pericyclic reactions that follow the Woodward-Hoffman rules. More significantly, asymmetric high-order dipolar annulations using chiral organometallic catalysts have been proven successful for constructing chiral medium-sized heterocycles with high enantio- and diastereoselectivity. This review highlights the impressive advances in this area and is focused on the reactivity, scope, mechanisms and applications of high-order dipolar annulation reactions.

Recent Advances in Decarboxylative Conversions of Cyclic Carbonates and Beyond

In recent years, functionalized cyclic organic carbonates have emerged as valuable building blocks for the construction of interesting and useful molecules upon decarboxylation under transition-metal catalysis. By employing suitable catalytic systems, the development of chemo-, regio-, stereo- and enantioselective methods for the synthesis of useful and interesting compounds has advanced greatly. On the basis of previous research on this topic, this short review highlights the synthetic potential of cyclic carbonates under transition-metal catalysis over the last two years.

1 Introduction

2 Transition-Metal-Catalyzed Decarboxylation of Vinyl Cyclic Carbonates

3 Zwitterionic Enolate Chemistry Based On Transition-Metal Catalysis

4 Decarboxylation of Alkynyl Cyclic Carbonates and Dioxazolones

5 Conclusions and Perspectives

Kinetically Controllable Construction of Nine-Membered Carbocycles via Pd-Catalyzed Decarboxylative Cycloaddition

A kinetically controllable strategy toward the construction of otherwise challenging nine-membered carbocycles is reported. This Pd-catalyzed decarboxylative procedure utilizes vinyl methylene cyclic carbonates as the C5-dipole and allylidenemalononitriles as C4-building blocks. The protocol features user-friendly operations with controllable regioselectivity and generates CO₂ as the sole byproduct. The formation of synthetically valuable and thermodynamically favored seven-membered carbocycles was also investigated.

Pd-Catalyzed Enantioselective (3+2)-Cycloaddition of Vinyl-Substituted Oxyallyl Carbonates with Isocyanates and Ketones

The vinyl-substituted oxyallyl carbonates were exploited as a new C,O-dipole for enantioselective Pd-catalyzed (3+2) cycloaddition. The corresponding oxyallyl-Pd species was weakly nucleophilic to react with activated carbonyl compounds, affording multisubstituted and enantioenriched oxazolidinones and 1,3-dioxolanes with a high degree of chemo- and stereoselectivity. The synthetic transformations of oxazolidinone product were carried out to build enantioenriched α-chiral aminoketone and epoxy derivatives.

Zwitterionic Metal-Enolate or Equivalent: Generation and Capture

Functionalized ketones and their derivatives are very important building blocks in organic synthesis and material chemistry. The development of novel methodology for the chemo-, regio-, diastereo-, stereo- and enantioselective synthesis of functionalized ketones and their derivatives is the continuous endeavor of organic chemists. Herein we highlight the new approach that was recently initiated and developed by our group for the synthesis of (enantioenriched) ketones and related derivatives based on zwitterionic metal-enolate (ZME) chemistry.

Regio- and enantioselective formation of tetrazole-bearing quaternary stereocenters via palladium-catalyzed allylic amination

A general and efficient method via catalysis by readily available Pd(0)/DACH-naphthyl catalyst under mild conditions, unlocks a new platform that permits the synthesis of elusive quaternary N2-allylic tetrazoles, even in the context of late-stage functionalization.

Selective approach to N-substituted tertiary 2-pyridones

Commercially available 2-hydroxypyridines are converted into enantiomerically enriched allylic 2-pyridones with elusive N-substituted tertiary carbon by means of Pd-catalyzed allylic amination of vinyl cyclic carbonates.

Pd-Catalyzed asymmetric decarboxylation for the construction of spiro[4.5]deca-6,9-dien-8-ones featuring vicinal quaternary carbons

A Pd-catalyzed decarboxylative strategy for the asymmetric construction of spiro[4.5]deca-6,9-dien-8-ones is reported. The epimerization of the resultant products occurred under otherwise Pd-catalysis.

Palladium-catalyzed stereoselective decarboxylative allylation of azlactones: access to (Z)-trisubstituted allylic amino acid derivatives

A palladium-catalyzed stereoselective decarboxylative allylation of azlactones with vinyl methylene cyclic carbonates affords a series of trisubstituted allylic amino acid derivatives in good yields with an exclusive (Z)-configuration.

Palladium-catalyzed decarboxylative [2 + 3] cyclocarbonylation reactions of [60]fullerene: selective synthesis of [60]fullerene-fused 3-vinylcyclopentan-4-ones and cyclopentane-4-carbaldehydes

A new palladium-catalyzed decarboxylative strategy has been developed toward direct cyclocarbonylation of [60]fullerene, selectively furnishing novel [60]fullerene-fused 3-vinylcyclopentan-4-ones and cyclopentane-4-carbaldehydes.

Palladium-catalysed stereoselective [3 + 2] annulation of vinylethylene carbonates and tryptanthrin-based ketones

The first example of palladium-catalysed [3 + 2] annulation of VECs and ketones has been developed, allowing the efficient synthesis of indoloquinazolinones in generally excellent yields with good stereoselectivity.

Computational Study on Homolytic Bond Energies of the Ag-X (X = C, O, and H) Complexes and Hammett-Type Analysis of Reactivity

Thirty-seven calculation methods were benchmarked against the available experimental bond lengths and energies data regarding the Ag-X bonds. The theoretical protocol PBE0/VDZ//ωB97x-D/mVTZ was found to be capable of accurately predicting the homolytic bond dissociation energies (BDEs) of Ag-X complexes with a precision of 1.9 kcal/mol. With the available method in hand, a wide range of different Ag-X BDEs were estimated. BDE(Ag-CH₂X), BDE(Ag-PhX), BDE(Ag-OPhX), and BDE(Ag-OCOPhX) (X = NH₂, OMe, Me, H, Cl, and NO₂) were found to be in the ranges of 27-47, 51-54, 19-39, and 64-70 kcal/mol, respectively. Subsequently, Hammett-type analysis was carried out with reactivity parameters. Good positive linear relationships were found for BDE of Ag-O bands and decarboxylation barriers of Ag-OCOPhX with the Hammett constant σ. It suggested that electron-donating substituents could promote either the homolytic cleavage of the Ag-OPhX bond to undergo a radical process or Ag-OCOPhX decarboxylation. Moreover, ligand effects on Ag-H bonds were investigated using BDE(Ag-H) and related NPA charges on Ag. In the case of P-ligands, carbene ligands, and other small molecule ligands (i.e., CO, CO₂, and H₂O), a good negative linear relationship was found. In contrast, N-ligands could have a reverse effect. Understanding the intrinsic relationships of BDE(Ag-X) with related reactivity parameters might help gain insights into the structure-reactivity relationships in Ag-X-assisted C-H activation/decarboxylation.

Ambiphilic Reactivity of Vinyl Pd-Oxyallyl for Expeditious Construction of Highly Functionalized Cyclooctanoids

We report the catalytic generation of a vinyl Pd-oxyallyl that dimerizes regiospecifically to form highly functionalized nonbridged cyclooctanoids. Such compounds are otherwise synthetically challenging, but highly useful in synthesis. This vinyl Pd-oxyallyl species demonstrates both electrophilic and nucleophilic properties. DFT calculations elucidate the mechanism and the origins of the chemoselective cyclooctanoid formation.

Diastereoselectivity-Switchable Gold-Catalyzed Formal [3+2]-Cycloadditions of N-2,2,2-Trifluoroethylisatin Ketimines with Yne-Enones

The unexpected gold-catalyzed formal [3+2]-cycloaddition of N-2,2,2-trifluoroethylisatin ketimines with 2-(1-Alkynyl)-2-alken-1-ones is reported. Both diastereomers of the corresponding cycloadducts were formed in moderate to excellent yields with excellent diastereoselectivities by switching the catalytic system from mono-gold to gold/silver bimetallic catalytic system. The practicality of this protocol is demonstrated by scale-up reaction and the transformations of the cycloadduct.

Palladium-Catalyzed (3+3) Annulation of Allenylethylene Carbonates with Nitrile Oxides

In this paper, we designed and synthesized a new type of cyclic carbonates, allenylethylene carbonates (AECs). With AECs as reactive precursors, we developed palladium-catalyzed (3+3) annulation of AECs with nitrile oxides. Various AECs worked well in this reaction under mild reaction conditions. A variety of 5,6-dihydro-1,4,2-dioxazine derivatives with allenyl quaternary stereocenters can be accessed in a facile manner in high yields (≤98%).

Ligand-Controlled Regiodivergent Asymmetric [5 + 2] and [3 + 2] Annulations of Vinyl Indoloxazolidones Catalyzed by Palladium

Here, we present palladium-catalyzed regiodivergent asymmetric annulations of vinyl indoloxazolidones, which can act as 1,5-carbodipoles or 1,3-carbodipoles by tuning the chiral ligands and conditions, in the assemblies with sulfamate-derived cyclic imines and even activated alkenes. A diversity of polycyclic products are generally constructed with high regio- and enantioselectivity.

Propargylic Amination Enabled the Access to Enantioenriched Acyclic α-Quaternary α-Amino Ketones

A propargylic amination approach toward chiral acyclic α-quaternary α-amino ketones is described. This Cu-catalyzed procedure could be performed open to air using commercially available amines as nucleophiles. The key to success is the use of rationally designed propargylic cyclic carbonates as substrates, which can generate a Cu-bonded enolate zwitterionic intermediate upon decarboxylation. This protocol features wide functional group tolerance and high asymmetric induction, with typical ee value higher than 93%, and thus advances a great step forward in the challenging synthesis of acyclic chiral α-quaternary α-amino ketones.

Access to azonanes via Pd-catalyzed decarboxylative [5 + 4] cycloaddition with exclusive regioselectivity

An efficient approach for the synthesis of azonanes via Pd-catalyzed decarboxylative [5 + 4] cycloaddition has been developed. The reactions feature wide functional group tolerance with exclusive regioselectivity.

Theoretical insight into the origins of chemo- and diastereo-selectivity in the palladium-catalysed (3 + 2) cyclisation of 5-alkenyl thiazolones

The mechanism of the palladium-catalysed (3 + 2) cyclisation of 5-alkenyl thiazolones and VECs has been investigated from a computational perspective, and the origins of unique chemoselectivity and excellent diastereoselectivity have been disclosed.

Pd/LA-catalyzed decarboxylation enabled exclusive [5 + 2] annulation toward N-aryl azepanes and DFT insights

A practical approach towards the synthesis of non-fused N-aryl azepane derivatives with diversity is described. DFT calculations revealed the origins of this unusual exclusive [5 + 2] rather than empirical [3 + 2] annulation process.