Ru-Catalyzed Asymmetric Hydrogenation of α,β-Unsaturated γ-Lactams

A highly efficient Ru-catalyzed asymmetric hydrogenation of α,β-unsaturated γ-lactams has been developed by using a C2-symmetric ruthenocenyl phosphine-oxazoline as the chiral ligand. This method achieves the enantioselective synthesis of chiral β-substituted γ-lactams in high yields and with excellent enantioselectivities (up to 99% yield with 99% ee). Mechanistic studies based on detailed control experiments and computational investigation revealed that the cationic Ru-complex acts as the active catalytic species; the protonation process of the oxa-π-allyl-Ru complex, which is formed by the migratory insertion of the C=C double bond to the Ru-H bond (the stereocontrolling step) followed by an isomerization process, is the rate-determining step, and the existence of PPh3 is crucial for the highly efficient catalytic behavior. The protocol provides a straightforward and practical pathway for the synthesis of key intermediates for several chiral drugs and bioactive compounds, particularly for the 150 kg-scale industrial production of Brivaracetam, an antiepileptic drug that shows 13-fold more potent binding to the synaptic vesicle protein 2A compared with the well-known Levetiracetam.

Asymmetric (3 + 3) and (4 + 2) Annulation Reactions of 2,3-Dioxopyrrolidines with 3-Alkylidene Oxindoles to Construct Diverse Chiral Heterocyclic Frameworks

Two substrate-controlled regiodivergent annulation protocols for 2,3-dioxopyrrolidines with 3-alkylidene oxindoles have been developed, which furnished a series of fused dihydropyrrolidone derivatives in high yields with excellent stereoselectivities. Plausible mechanistic pathways for both annulation reactions are proposed that [3 + 3] annulation reaction involves vinylogous Michael addition followed by intramolecular aldol cyclization, while [4 + 2] annulation reaction occurs through a vinylogous Michael addition and a subsequent intramolecular oxa-Michael cyclization.

Thiophene-fused γ-lactams inhibit the SARS-CoV-2 main protease via reversible covalent acylation

Enzyme inhibitors working by O-acylation of nucleophilic serine residues are of immense medicinal importance, as exemplified by the β-lactam antibiotics. By contrast, inhibition of nucleophilic cysteine enzymes by S-acylation has not been widely exploited for medicinal applications. The SARS-CoV-2 main protease (Mpro) is a nucleophilic cysteine protease and a validated therapeutic target for COVID-19 treatment using small-molecule inhibitors. The clinically used Mpro inhibitors nirmatrelvir and simnotrelvir work via reversible covalent reaction of their electrophilic nitrile with the Mpro nucleophilic cysteine (Cys145). We report combined structure activity relationship and mass spectrometric studies revealing that appropriately functionalized γ-lactams can potently inhibit Mpro by reversible covalent reaction with Cys145 of Mpro. The results suggest that γ-lactams have potential as electrophilic warheads for development of covalently reacting small-molecule inhibitors of Mpro and, by implication, other nucleophilic cysteine enzymes.

Dual Photoredox/Nickel Catalysis Enables Diastereoselective Synthesis of Multisubstituted γ-Lactams Using Alkyl-GeMe3 as Radical Precursors

Herein, we report a single-step, multicomponent approach to versatile γ-lactams through dual photoredox/nickel-catalyzed dicarbofunctionalization of α,β-unsaturated γ-butyrolactam. This reaction utilized alkyl trimethylgermanium as a radical precursor and acyl chloride as the electrophile, demonstrating remarkable functional group compatibility.

Photoredox/Copper-Catalyzed One-Pot Aminoalkylation/Cyclization of Alkenes with Primary Amines to Synthesize Polysubstituted γ-Lactams

Visible-light-driven chemical transformation has emerged as a powerful tool for the synthesis of γ-lactams. However, during this transformation, the α-bromoimides need to be pre-prepared. Herein, we report a photoreodox/copper-catalyzed one-pot three-component reaction of alkenes with primary amines for the construction of γ-lactams. In this transformation, the orthoquinones were generated via a photocatalytic pathway, followed by attack by Cu-amido complexes and intramolecular cyclization to give the γ-lactams. This method represents a simple synthetic route displaying broad functional group tolerance, including substrates bearing alcohols, ketones, heterocycles, esters, halides, alkynes, nitriles, ethers, etc.

One-Pot, Tandem Reductive Amination/Alkylation-Cycloamidation for Lactam Synthesis from Keto or Amino Acids

Monotrifluoroacetoxyborane-amines, prepared by treating borane-amines with trifluoroacetic acid, have been shown to be efficient reagents for a one-pot, tandem reductive amination/alkylation-cycloamidation of keto or amino acids to achieve the synthesis of 5-aryl or 5-methyl pyrrolidin-2-ones and 6-aryl or 6-methyl piperidin-2-ones.

Et2Zn-Mediated Radical (3 + 2) Cycloaddition of Vinyl Azides with Ethyl Iododifluoroacetate to Access 3,3-Difluoro-γ-lactams

A diethylzinc-mediated radical (3 + 2) cycloaddition of vinyl azides with ethyl iododifluoroacetate is presented. The developed reaction features good functional group tolerance, broad substrate scope, and operational simplicity, enabling efficient assembly of a wide range of 3,3-difluoro-γ-lactam derivatives bearing an O-substituted quaternary carbon center in moderate to good yields. The utility of the method is showcased by a scaled-up reaction, conversion of the product, and late-stage structural modifications of a variety of pharmaceutical compounds.

Asymmetric Construction of Multifunctional γ-Lactams from 1,3-Dienes and α-Ketoamides via Pd(0)-π-Lewis Base Catalysis

A straightforward approach for the asymmetric synthesis of multifunctionalized γ-lactams, including those bearing two tetrasubstituted stereogenic centers, has been developed through a palladium-catalyzed vinylogous addition/allylic amination process between 1,3-dienes and α-ketoamides. This protocol features advantages of ready substrate availability, broad applicability, high efficiency, and excellent stereoselectivity, making it an attractive complementary tool to the previous strategies.

Enantioselective 1,3-Dipolar Cycloadditions of α-Methylene Lactams to Construct Spirocycles

Spirocyclic scaffolds are important motifs due to their potential to bestow favorable effects on pharmaceutical compounds. However, there is a need for efficient methods for their enantioselective construction. We report a method for the asymmetric 1,3-dipolar cycloaddition of diazoacetates or nitrile oxides with α-methylene lactams to prepare chiral spirocyclic heterocycles. The methodology is high yielding (up to 91% yield) and enantioselective (up to 89% ee) for a wide range of N-substituents and 6- and 7-membered ring lactam substrates.

Mannich-type addition of cyclic 1,3-diketones to N-acyliminium ions: Access to aza-sugars

A novel three-component strategy has been developed for the synthesis of iminosugars in good to excellent yields. This is the first report on the Mannich type addition of cyclic 1,3-diketones to aza-acetal derived from hydroxy-γ-lactone and arylamine to produce a novel series of aza-sugars with high selectivity.

Copper-Catalyzed Sulfonylation/Cyclization of Pent-4-ynamides toward Sulfonyl-Functionalized Pyrrol-2-ones

A domino sulfonylation/intramolecular C-N coupling/dehydrogenation reaction was realized between pent-4-ynamides and sulfonyl chlorides by catalysis of Cu(acac)₂ and 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthalene. The reaction provides a convenient approach to sulfonyl-functionalized pyrrol-2-ones. This method can also be applied to the synthesis of 3-alkylidene isoindolinones from 2-ethynyl-benzamides.

Cooperative Isothiourea/Iridium-Catalyzed Asymmetric Annulation Reactions of Vinyl Aziridines with Pentafluorophenyl Esters

Chiral γ-lactam-containing skeletons are important motifs in bioactive natural products, pharmaceuticals, and bioactive molecules. Herein, we report a general and modular platform to access chiral γ-lactam compounds via an ITU/Ir cooperatively catalyzed [3 + 2] asymmetric annulation reaction of vinyl aziridines with pentafluorophenyl esters. Through the Lewis base and transition metal cooperative catalytic regime, a broad range of optically active γ-lactams were generated in good yields (up to 92%) with high asymmetric induction (up to 98% ee). Furthermore, the utility of this synthetic protocol was also demonstrated by the expedient preparation of diverse enantioenriched architectures.

Copper-Catalyzed Diastereo- and Enantioselective Decarboxylative [3 + 2] Cyclization of Alkyne-Substituted Cyclic Carbamates with Azlactones: Access to γ-Butyrolactams Bearing Two Vicinal Tetrasubstituted Carbon Stereocenters

A copper-catalyzed diastereo- and enantioselective decarboxylative [3 + 2] cyclization reaction of alkyne-substituted cyclic carbamates with azlactones has been established. A range of optically pure γ-butyrolactams bearing two vicinal tetrasubstituted carbon stereocenters were obtained in high yields with good to excellent stereoselectivities (up to 99% yield, 99:1 dr, and 99% ee). This is the first example of asymmetric synthesis γ-butyrolactams containing sterically congested vicinal tetrasubstituted stereocenters via a decarboxylative cyclization pathway.

K2S2O8-Mediated Radical Cyclization of 1,6-Enyne for the Synthesis of Diiodonated γ-Lactams

A novel and convenient K₂S₂O₈-mediated diiodo cyclization of 1,6-enynes for the facile synthesis of functionalized γ-lactam derivatives has been developed. This reaction features mild and transition-metal-free conditions, which offer a green and efficient entry to synthetically important γ-lactam scaffolds. Mechanistic studies suggest that iodide radicals initiate the cascade cyclic transformation.

Coupling of α-bromoamides and unactivated alkenes to form γ-lactams through EDA and photocatalysis

γ-Lactams are prevalent in small-molecule pharmaceuticals and provide useful precursors to highly substituted pyrrolidines. Despite numerous methods for the synthesis of this valuable motif, previous redox approaches to γ-lactam synthesis from α-haloamides and olefins require additional electron withdrawing functionality as well as N-aryl substitution to promote electrophilicity of the intermediate radical and prevent competitive O-nucleophilicity about the amide. Using α-bromo imides and α-olefins, our strategy enables the synthesis of monosubstituted protected γ-lactams in a formal [3 + 2] fashion. These species are poised for further derivatization into more complex heterocyclic scaffolds, complementing existing methods. C-Br bond scission occurs through two complementary approaches, the formation of an electron donor-acceptor complex between the bromoimide and a nitrogenous base which undergoes photoinduced electron transfer, or triplet sensitization with photocatalyst, to furnish an electrophilic carbon-centered radical. The addition of Lewis acids allows for further increased electrophilicity of the intermediate carbon-centered radical, enabling tertiary substituted α-Br-imides to be used as coupling partners as well as internal olefins.

Phosphazene Base-Catalyzed Intramolecular Hydroamidation of Alkenes with Amides

A method for the synthesis of cyclic amides via phosphazene base-catalyzed intramolecular hydroamidation of amide alkenes was developed. The reaction using a catalytic amount of P4-base had a good functional group tolerance and a broad substrate scope and could also be used to synthesize lactam, cyclic urea, and oxazolidinone compounds. This catalytic system was expanded to a one-pot intramolecular hydroamidation and intermolecular hydroalkylation. Deuterium labeling and radical trapping experiments provided mechanistic insights into the catalytic cycle of the hydroamidation reaction.

Synthesis of Trifluoromethylated γ-Lactams through Radical Cascades of N-Cyano Alkenes with CF3SO2Na

We report herein a facile strategy to synthesize trifluoromethylated γ-lactams through trifluoromethylcarbonylation of N-cyano alkenes using readily available CF₃SO₂Na as the CF₃ radical source. A range of trifluoromethyl-containing γ-lactams was obtained in good yields. This transition-metal-free protocol is demonstrated with mild conditions, broad substrate scope, good functional group tolerance, convenient reagents, and an easy-to-handle operating system.

Substrate-Dependent Selectivity in Sc(OTf)3-Catalyzed Cyclization of Alkenoic Acids and N-Protected Alkenamides

Five- and six-membered ring lactones and lactams are ubiquitous frameworks in various natural and synthetic molecules and are key building blocks in organic synthesis. Catalytic addition of an O-H or N-H bond across an unactivated C–C double bond is an appealing approach to rapidly access such highly valuable N- and O-containing skeletons in a waste-free and 100% atom efficient process. Herein, we report, for the first time, the efficient and high-yield cyclization of δ/ε-alkenoic acids and N-protected δ-alkenamides catalyzedby practical and easily accessible Lewis acid scandium(III) triflate under thermal and microwave conditions. The selectivity outcome of the reaction of δ/ε-alkenoic acids was dependent on the substitution patterns of the backbone chain and alkene moiety, leading to the exclusive formation of either the corresponding γ/δ-lactones via an O-selective cyclization or the Friedel–Crafts-type product by C-selective cyclization. An uncommon and rarely disclosed O-selective cyclization occurred preferentially or exclusively when N-protected δ-alkenamides were engaged in the reaction. The atom selectivity of the cyclization was unambiguously confirmed by single crystal X-ray crystallography.

Ni-catalyzed carbamoylation of unactivated alkenes for stereoselective construction of six-membered lactams

Nitrogen-based heterocycles have aroused widespread interest due to their reoccurrence in many pharmaceuticals. Amongst these motifs, the enantioenriched lactams are the ubiquitous scaffolds found in myriad biologically active natural products and drugs. Recently, the transition metal-catalyzed asymmetric carbamoylation has been widely employed as a straightforward arsenal for chiral lactam architecture synthesis, including β-lactam and γ-lactam. However, despite the extensive efforts, there still remains no protocol to accomplish the related δ-lactam synthesis. In this manuscript, the Ni-catalyzed enantioselective carbamoylation of unactivated alkenes by the leverage of reductive dicarbofunctionalization strategy allows for the expedient access to two types of mostly common six-membered lactams: 3,4-dihydroquinolinones and 2-piperidinone in high yield and enantioselectivity. This protocol features with good functional group tolerance, as well as broad substrate scope. The newly developed chiral 8-Quinox skeleton ligand is the key parameter for this transformation, which significantly enhances the reactivity and enantioselectivity.

Nickel-Catalyzed Enantioselective Reductive Alkyl-Carbamoylation of Internal Alkenes

Herein, we leverage the Ni-catalyzed enantioselective reductive dicarbofunctionalization of internal alkenes with alkyl iodides to enable the synthesis of chiral pyrrolidinones bearing vicinal stereogenic centers. The application of newly developed 1-Nap Quinim is critical for formation of two contiguous stereocenters in high yield, enantioselectivity, and diastereoselectivity. This catalytic system also improves both the yield and enantioselectivity in the synthesis of α,α-dialkylated γ-lactams. Computational studies reveal that the enantiodetermining step proceeds with a carbamoyl-NiI intermediate that is reduced by the Mn reductant prior to intramolecular migratory insertion. The presence of the t-butyl group of the Quinim ligand leads to an unfavorable distortion of the substrate in the TS that leads to the minor enantiomer. Calculations also support an improvement in enantioselectivity with 1-Nap Quinim compared to p-tol Quinim.

Catalytic Desymmetric Dicarbofunctionalization of Unactivated Alkenes

The construction of multi-stereocenters by a transition metal-catalyzed cross-coupling reaction is a major challenge. The catalytic desymmetric functionalization of unactivated alkenes remains largely unexplored. Herein, we disclose -a desymmetric dicarbofunctionalization of 1,6-dienes via a nickel-catalyzed reductive cross-coupling reaction. The leverage of the underdeveloped chiral 8-Quinox enables the Ni-catalyzed desymmetric carbamoylalkylation of both unactivated mono- and disubstituted alkenes to form pyrrolidinone bearing two nonadjacent stereogenic centers in high enantio- and stereoselectivitives with broad functional-group tolerance. The synthetic application of pyrrolidinones allows the rapid access to complex chiral fused-heterocycles.

Highly Diastereoselective Synthesis of γ-Lactams Enabled by Photoinduced Deaminative [3 + 2] Annulation Reaction

The photoinitiated deaminative [3 + 2] annulation reaction of N-aminopyridinium salts with alkenes for the synthesis of functionalized γ-lactams is described. This transformation shows good functional group tolerance as well as excellent diastereoselectivity. Preliminary studies suggest that the employed N-aminopyridinium salts generate the key amidyl radical intermediates through N-N bond cleavage via a photoinduced single-electron transfer (SET) process. The amidyl radical species would add to the double bond of alkenes, followed by a radical-mediated annulation process, to afford the desired γ-lactams.

Exploring the Synthetic Potential of γ-Lactam Derivatives Obtained from a Multicomponent Reaction. Applications as Antiproliferative Agents

A study on the reactivity of 3-amino α,β-unsaturated γ-lactam derivatives obtained from a multicomponent reaction is presented. Key features of the substrates are the presence of an endocyclic α,β-unsaturated amide moiety and an enamine functionality. Following different synthetic protocols, the functionalization at three different positions of the lactam core is achieved. In the presence of a soft base, under thermodynamic conditions, the functionalization at C-4 takes place where the substrates behave as enamines, while the use of a strong base, under kinetic conditions, leads to the formation of C-5-functionalized γ-lactams, in the presence of ethyl glyoxalate, through a highly diastereoselective vinylogous aldol reaction. Moreover, the nucleophilic addition of organometallic species allows the functionalization at C-3, through the imine tautomer, affording γ-lactams bearing tetrasubstituted stereocenters, where the substrates act as imine electrophiles. Taking into account the advantage of the presence of a chiral stereocenter in C-5 substituted γ-lactams, further diastereoselective transformations are also explored, leading to novel bicyclic substrates holding a fused γ and δ-lactam skeleton. Remarkably, an example of a highly stereoselective formal [3+3] cycloaddition reaction of chiral γ-lactam substrates is reported for the synthesis of 1,4-dihidropyridines, where a non-covalent attractive interaction of a carbonyl group with an electron-deficient arene seems to drive the stereoselectivity of the reaction to the exclusive formation of the cis isomer. In order to unambiguously determine the substitution pattern resulting from the diverse reactions, an extensive characterization of the substrates is detailed through 2D NMR and/or X-ray experiments. Likewise, applications of the substrates as antiproliferative agents against lung and ovarian cancer cells are also described.

Amino-Functionalized Multiwall Carbon Nanotubes as Efficient Basic Catalysts for the Formation of γ-Lactams: Synthesis of N-1-Heptenyl-2-Pyrrolidinone

In this work, we prepared a series of N-functionalized carbon nanotubes by means of a process of acylation-amidation of commercial multiwall carbon nanotubes that were previously pre-oxidized with nitric acid. Three different amines, butylamine, N,N-dimethyl ethylenediamine, and ethylenediamine, were used in the process. The characterization of samples by several techniques probed the incorporation of nitrogen atoms to the carbon nanotubes, especially in the case of ethylenediamine. The solids were tested as catalysts in the synthesis of N-1-heptenyl-2-pyrrolidinone, included in the group of a γ-lactams, compounds that show important biological properties. The most active catalyst was that prepared with butylamine, which exhibited the highest S_BET and V_pore values and contained an amount of nitrogen that was intermediate between that of the other two catalysts. A yield of 60% to N-1-heptenyl-2-pyrrolidinone was achieved after 3 h at 120 °C under free-solvent conditions. This catalyst could be used in four consecutive cycles without significant activity loss.

Trans-selective cyclizations of alpha-bromocarboxamides and E/Z-mixed internal olefins catalyzed by a Fe salt

Herein, we describe a protocol for trans-selective cyclizations of α-bromocarboxamides and E/Z-mixed internal olefins catalyzed by a Fe salt.

Synthesis of γ-amino acids via photocatalyzed intermolecular carboimination of alkenes

We report a direct approach to achieve the energy transfer-driven carboimination of alkenes for the synthesis of a diverse collection of valuable γ-amino acids.

Ligand Enabled Pd(II)-Catalyzed γ-C(sp3)-H Lactamization of Native Amides

γ-Lactams form important structural cores of a range of medicinally relevant natural products and clinical drugs, principal examples being the new generation of immunomodulatory imide drugs (IMiDs) and the brivaracetam family. Compared to conventional multistep synthesis, an intramolecular γ-C-H amination of aliphatic amides would allow for the direct construction of valuable γ-lactam motifs from abundant amino acid precursors. Herein we report a novel 2-pyridone ligand enabled Pd(II)-catalyzed γ-C(sp³)-H lactamization of amino acid derived native amides, providing the convenient synthesis of γ-lactams, isoindolinones, and 2-imidazolidinones. C6-Substitution of the 2-pyridone ligand is crucial for the lactam formation. This protocol features the use of N-acyl amino acids, which serve as both the directing group and cyclization partner, practical and environmentally benign tert-butyl hydrogen peroxide (TBHP) as the sole bystanding oxidant, and a broad substrate scope. The utility of this protocol was demonstrated through the two-step syntheses of a lenalidomide analog and brivaracetam from readily available carboxylic acids and amino acids.

Reductive Recyclization of sp3-Enriched Functionalized Isoxazolines into α-Hydroxy Lactams

An efficient synthesis (up to a 200 g scale) of 3-hydroxypyrrolidin-2-ones bearing alkyl substituents or functional groups at the C-5 position is described. The reaction sequence started from 1,3-dipolar cycloaddition of in situ generated nitrile oxides with (meth-)acrylates into 3-substituted isoxazoline-5-carboxylates. The catalytic hydrogenolysis of the isoxazoline N-O bond was optimal upon using H₂ (1 atm) at rt, with the following order of the catalyst activity: Pd-C > Pd(OH)₂-C > Pt-C. The reactions with Pt-C were more selective for the synthesis of pyrrolidones, while Pd-C provided the fastest conversion rates. The stirring efficiency had a positive impact on conversion rather than elevated temperatures (up to 40 °C) or pressure (up to 50 atm). The diastereoselectivity was governed mainly by steric factors, with a dr of 1:1 to 3:1 (cis- and trans-isomers could be separated). Higher homologues (isoxazolinylacetates and -propanoates) were suitable for the synthesis of 6- or 7-substituted 4-hydroxypiperidones and 5-hydroxyazepanones, respectively. The proposed methods are tolerant to functional groups, including CF₃ (but not CHF₂ or CH₂Cl), ester, and most N-Boc-protected amines. The utility of hydroxyl groups in lactams was shown by functional group transformations. Hydrogenolysis of C(5)-functionalized isoxazolines, bearing trimethylsilyl, phosphonate, or sulfone groups, was also studied to demonstrate limitations.

Photoredox-Catalyzed Difunctionalization of Unactivated Olefins for Synthesizing Lactam-Substituted gem-Difluoroalkenes

Herein, the synthesis of lactam-substituted gem-difluoroalkenes has been developed through a photoredox-catalyzed radical cascade reaction. This developed photoredox-catalyzed, Brønsted base-assisted intramolecular 5-exo-trig cyclization/intermolecular radical addition/β-fluoride elimination reaction offers a simple method for producing lactam, carbamate, or urea-substituted gem-difluoroalkenes with good functional group tolerance and high yields.

Enantioselective Hydroesterificative Cyclization of 1,6-Enynes to Chiral γ-Lactams Bearing a Quaternary Carbon Stereocenter

A palladium-catalyzed asymmetric hydroesterification-cyclization of 1,6-enynes with CO and alcohol was developed to efficiently prepare a variety of enantioenriched γ-lactams bearing a chiral quaternary carbon center and a carboxylic ester group. The approach featured good to high chemo-, region-, and enantioselectivities, high atom economy, and mild reaction conditions as well as broad substrate scope. The correlation between the multiple selectivities of such process and the N-substitutes of the amide linker in the 1,6-enyne substrate has been depicted by the crystallographic evidence and control experiments.

Photoredox-Catalyzed α-Aminomethyl Carboxylation of Styrenes with Sodium Glycinates: Synthesis of γ-Amino Acids and γ-Lactams

A visible-light photoredox-catalyzed reductive α-aminomethyl carboxylation of styrenes with sodium glycinates and CO₂ has been developed to synthesize a series of α,α-disubstituted γ-amino acids and γ-lactams with high efficiency and regioselectivity. Notably, CO₂ released from the decarboxylation step can be reused for the subsequent carboxylation. Distinct from the previous reactions with the same type of substrates leading to simple decarboxylation and olefin hydroalkylation, this process involves additional CO₂ sequestration, thus leading to olefin α-aminomethyl carboxylation. These findings not only provide new access to α,α-disubstituted γ-amino acids and γ-lactams but also serve as a proof of concept for CO₂ reutilization in decarboxylation reactions.

1,2-Aryl Migration Induced by Amide C-N Bond-Formation: Reaction of Alkyl Aryl Ketones with Primary Amines Towards α,α-Diaryl β,γ-Unsaturated γ-Lactams

Rearrangement reactions incorporated into cascade reactions play an important role in rapidly increasing molecular complexity from readily available starting materials. Reported here is a Cu-catalyzed cascade reaction of α-(hetero)aryl-substituted alkyl (hetero)aryl ketones with primary amines that incorporates an unusual 1,2-aryl migration induced by amide C-N bond formation to produce a class of structurally novel α,α-diaryl β,γ-unsaturated γ-lactams in generally good-to-excellent yields. This cascade reaction has a broad substrate scope with respect to primary amines, allows a wide spectrum of (hetero)aryl groups to smoothly undergo 1,2-migration, and tolerates electronically diverse α-substituents on the (hetero)aryl ring of the ketones. Mechanistically, this 1,2-aryl migration may stem from the intramolecular amide C-N bond formation which induces nucleophilic migration of the aryl group from the acyl carbon center to the electrophilic carbon center that is conjugated with the resulting iminium moiety.

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

Pyrrolidones are common heterocyclic fragments in various biologically active compounds. Here, a two-step radical-based approach to γ-lactams bearing three to four stereocenters starting from epoxides, N-allylic silylacetamides and TEMPO is reported. The sequence starts with a new tandem nucleophilic substitution/Brook rearrangement/single electron transfer-induced radical oxygenation furnishing orthogonally protected α,γ-dioxygenated N-allylamides with wide scope, mostly good yields, and partly good diastereo- and enantioselectivity for defined combinations of chiral epoxides and chiral amides. This represents a very rare example of an oxidative geminal C-C/C-O difunctionalization next to carbonyl groups. The resulting dioxygenated allylic amides are subsequently subjected to persistent radical effect-based 5-exo-trig radical cyclization reactions providing functionalized pyrrolidones in high yields as diastereomeric mixtures. They converge to 3,4-trans-γ-lactams by base-mediated equilibration, which can be easily further diversified. Stereochemical models for both reaction types were developed.

Regio-, Chemo-, and Enantioselective Ni-Catalyzed Hydrocyanation of 1,3-Dienes

A regio-, chemo-, and enantioselective nickel-catalyzed hydrocyanation of 1,3-dienes is reported. The key to the success of this asymmetric transformation is the use of a specific multichiral diphosphite ligand. In addition to aryl-substituted 1,3-dienes, highly challenging aliphatic 1,3-diene substrates can also be preferentially converted to the corresponding 1,2-adducts in decent yields with the highest enantioselectivities to date.

Brønsted Base-Catalyzed Formal Reductive [3+2] Annulation of 4,4,4-Trifluorocrotonate and α-Iminoketones

A formal reductive [3+2] annulation of 4,4,4-trifluorocrotonate and α-iminoketones was developed under Brønsted base catalysis. A single phosphazene base efficiently catalyzes the one-pot tandem reaction involving two mechanistically different elementary processes, namely the chemoselective reduction of an imine moiety of α-iminoketones with thiols as the reductant and the subsequent intermolecular Michael addition of an enolate of α-aminoketones concomitant with lactam formation. This operationally simple method provides β-trifluoromethyl-substituted γ-lactams with a tetrasubstituted carbon as a single diastereomer.

Strategies and methodologies for the construction of spiro-γ-lactams: an update

This review gives an insight into the most recent synthetic methodologies towards spiro-γ-lactams, a class of compounds that are present in a wide range of synthetic bioactive and naturally occurring molecules.