Diastereoselective Palladium-Catalyzed (3 + 2)-Cycloadditions from Cyclic Imines and Vinyl Aziridines

Cycloadditions of 5-Vinyloxazolidine-2,4-diones: A Straightforward Access to the (Thio)hydantoin Scaffold

A palladium-catalyzed (3 + 2) cycloaddition between 5-vinyloxazolidine-2,4-diones (VOxD) and (thio)isocyanates is described. Under optimized conditions, an array of (thio)hydantoins was readily prepared, and an enantioselective version of this transformation was then studied. To illustrate the importance of this method, a concise synthesis of two bioactive compounds, nirvanol and mephenytoin, was carried out. This work emphasizes the synthetic potential of VOxD as useful precursors of zwitterionic aza-π-allylpalladiumII intermediates.

Base mediated aza-[2 + 1] annulation and regioselective aziridine ring-opening cascade: mild synthesis of functionalized β-amino ketones from cyclic N-sulfonyl aldimines and α-carbonyl sulfonium salts

Cyclic N-sulfonyl aldimines are well-known aza-[2C]-synthons for various [2 + n] annulation reactions. Herein we describe a novel base mediated [2 + 1] annulation and a regioselective aziridine ring-opening reaction cascade, which provides an efficient and distinct synthetic strategy from readily available cyclic N-sulfonyl aldimines and α-carbonyl sulfonium salts leading to β-amino ketone derivatives through the corresponding fused tri-substituted aziridines. This one-pot, two-step process involves formation of C-C and C-N bonds and subsequent cleavage of a C-N bond. The features of the developed reaction include the use of mild reaction conditions, broad substrate scope, and excellent yields. The synthetic utility of this approach was demonstrated by gram-scale operation and further product derivatizations.

Copper-catalyzed reaction of aziridine for the synthesis of substituted imidazolidine and imidazolidinone

Herein we report a copper-catalyzed synthesis of imidazolidine by employing the reaction of aziridine with imine. The reaction smoothly provided a diverse range of 2-substituted imidazolidines with high compatibility with various functional groups. Moreover, during our investigation, we discovered that isocyanate also reacted with aziridine to yield substituted imidazolidinones efficiently. The versatility of these reactions was further demonstrated by their application in the synthesis of hybrid molecules derived from two pharmaceutical compounds. This approach opens new possibilities for the discovery of novel classes of bioactive molecules.

Diastereo- and Enantioselective Palladium-Catalyzed Cycloadditions of 5-Vinyloxazolidine-2,4-diones with Electrophilic Imines

Despite the importance of the 4-imidazolidinone scaffold in bioactive compounds or organocatalysts, methodologies to access these nitrogenated heterocycles remain scarce. This manuscript describes a novel preparation of 4-imidazolidinones via a diastereo- and enantioselective (3 + 2) cycloaddition between 5-vinyloxazolidine-2,4-diones (VOxD) and electrophilic imines under palladium catalysis. This work supports the synthetic potential of VOxD as a promising equivalent of the C-C(═O)-N synthon.

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.

Swapping Copper-Catalytic Process: Selective Access to Pyrazoles and Conjugated Ketimines from Oxime Acetates and Cyclic Sulfamidate Imines

A powerful CuCl-catalyzed sequential one-pot reaction of aryl methyl ketoxime acetates with cyclic N-sulfonyl imines followed by elimination in the presence of base is reported. This hydrazine-free method conveniently makes C-C and N-N bonds via a radical cleavage of the N-O bond, delivering a special class of C3-hydroxyarylated pyrazoles in good yields. Surprisingly, while employing CuI as a catalyst instead of CuCl, the reaction proceeds through a non-radical pathway which embodies a new tactic for the high-yielding access to value-added conjugated N-unsubstituted ketimines. Moreover, additive-free approach to sulfamidate-fused-pyrazoles was achieved by successfully catalyzing addition and oxidative N-N bond-making reactions by CuI and CuCl, respectively. Significantly, our novel technique could convert the prepared ketimines into the pharmacologically recognized 6H-benzo[c]chromene frameworks.

Enantioselective [3+2] Cycloaddition of Donor-Acceptor Aziridines and Imines to Construct 2,5-trans-Imidazolidines

An enantioselective [3+2] cycloaddition of donor-acceptor aziridines with N-aryl protected imines was developed with a Ni(ClO₄ )₂  ⋅ 6H₂ O/N,N'-dioxide catalyst system, providing a broad range of chiral trans-substituted imidazolidine compounds with good yields and excellent enantioselectivities (up to 99 % yield, up to 98 % ee). Control experiments indicated that the products could offer excellent diastereoselectivities with the control of chiral Ni(II)-N,N'-dioxide complex and the interaction of the substrates. The possible catalytic process was proposed to rationalize the stereocontrol.

Palladium-Catalyzed Carbonylative [5+1] Cycloaddition of N-Tosyl Vinylaziridines: Solvent-Controlled Divergent Synthesis of α,β- and β,γ-Unsaturated δ-Lactams

A palladium-catalyzed carbonylative [5+1] cycloaddition of N-tosyl vinylaziridines with CO has been developed. This protocol affords an efficient and practical approach for solvent-controlled divergent synthesis of α,β-unsaturated δ-lactams in dimethylformamide and β,γ-unsaturated δ-lactams in tetrahydrofuran in good to excellent yields. Significantly, the step- and atom-economical reactions are more regioselective toward [5+1] cycloaddition than toward [3+1] cycloaddition.

Visible-light-induced cyclization of cyclic N-sulfonyl ketimines to N-sulfonamide fused imidazolidines

A visible-light-induced metal-free cascade cyclization of cyclic N-sulfonyl ketimines with N-arylglycines for the construction of N-sulfonamide-fused imidazolidines was developed. The procedure employed 3 mol% of eosin Y as the photocatalyst at room temperature under visible light irradiation, providing various N-sulfonamide-fused imidazolidines in good yields (32 examples, up to 86% yields).

Efficient synthesis of benzosultams containing continuous quaternary carbons via trapping active ylides with cyclic N-sulfonyl ketimines

A rapid and efficient method for the synthesis of benzosultams containing continuous quaternary carbons in a one pot fashion has been developed with moderate to excellent yields at room temperature under air. The resulting products exhibit good anticancer activity in osteosarcoma cells.

Nickel-Catalyzed Asymmetric Hydrogenation for Kinetic Resolution of [2.2]Paracyclophane-Derived Cyclic N-Sulfonylimines

Nickel-catalyzed asymmetric hydrogenation for kinetic resolution of [2.2]paracyclophane-derived cyclic N-sulfonylimines was successfully developed. High selectivity factors were observed in most cases (s up to 89), providing the recovered materials and hydrogenation products in good yields with high levels of enantiopurity. The recovered materials and hydrogenation products are useful synthetic intermediates for the synthesis of planar chiral [2.2]paracyclophane-based compounds.

The transition-metal-catalyzed stereoselective ring-expansion of vinylaziridines and vinyloxiranes

The transition-metal-aided stereoselective construction of sp3-carbon-rich heterocyclic scaffolds using strained-ring systems has received considerable attention in recent years due to the prominent presence of these scaffolds in myriad natural products, bioactive molecules, and pharmaceutical components. In this area, the catalytic ring-enlargement of vinylaziridines and vinyloxiranes plays a predominant role when synthesizing high sp3-content biorelevant heterocyclic compounds. This article aims to portray recent advancements in the ring-expansion of vinylaziridines and vinyloxiranes for accessing densely functionalized stereoselective heterocycles that have been developed over the past five years, with an emphasis on the substrate scopes and mechanistic insights into the key methodologies, and it is arranged based on the transition metals used and the ring sizes of the heterocyclic scaffolds.

An organophotoredox-catalyzed C(sp2)-N cross coupling reaction of cyclic aldimines with cyclic aliphatic amines

An organophotocatalyzed C(sp2)-H/N-H cross-dehydrogenative coupling of cyclic aldimines with aliphatic amines has been developed, which represents the first example of visible-light-induced C-H amination of N-sulfonylated imines. This methodology enables the streamline assembly of amine derivatives via radical mediated C-N bond formation. The current protocol features transition-metal-free, mild conditions, good functional group tolerance and good yields.

Ag-Catalyzed ring-opening of tertiary cycloalkanols for C-H functionalization of cyclic aldimines

We firstly describe a silver-catalyzed direct C-H functionalization of cyclic aldimines with cyclopropanols and cyclobutanols via a radical-mediated C-C bond cleavage strategy. The desired products were generated in decent yields with wide substrate scope under mild reaction conditions. In addition, a gram-scale reaction and synthetic transformation of the product were performed.

Recent advances in annulation reactions based on zwitterionic π-allyl palladium and propargyl palladium complexes

Carbocyclic and heterocyclic compounds could be constructed through the palladium-catalyzed annulation reactions of zwitterionic π-allyl palladium or propargyl palladium complexes with unsaturated electrophiles.

Visible-Light Photoredox-Catalyzed Formal [5 + 1] Cycloaddition of N-Tosyl Vinylaziridines with Difluoroalkyl Halides

A visible-light photoredox-catalyzed formal [5 + 1] cycloaddition of N-tosyl vinylaziridines with difluoroalkyl halides as unique C1 synthons was developed. The procedure provides an efficient and practical method to synthesize diverse pyridines in moderate to good yields. The reaction underwent a radical-initiated kinetically controlled ring-opening of vinylaziridines and involved a key α,β-unsaturated imine intermediate, followed by an E2 elimination, a 6π electrocyclization, and defluorinated aromatization.

Accelerated Reactivity Mechanism and Interpretable Machine Learning Model of N-Sulfonylimines toward Fast Multicomponent Reactions

We introduce chemical reactivity flowcharts to help chemists interpret reaction outcomes using statistically robust machine learning models trained on a small number of reactions. We developed fast N-sulfonylimine multicomponent reactions for understanding reactivity and to generate training data. Accelerated reactivity mechanisms were investigated using density functional theory. Intuitive chemical features learned by the model accurately predicted heterogeneous reactivity of N-sulfonylimine with different carboxylic acids. Validation of the predictions shows that reaction outcome interpretation is useful for human chemists.

Synergistic Palladium-Phosphoric Acid Catalysis in (3 + 2) Cycloaddition Reactions between Vinylcyclopropanes and Imines

The palladium-catalyzed (3 + 2) cycloaddition reaction between vinylcyclopropanes (VCPs) bearing geminal EWG’s and imines represents a straightforward and flexible entry to polysubstituted pyrrolidine derivatives. In this paper, we demonstrate that using a synergistic catalysis approach, based on the combination of phosphoric acid and palladium catalysts, it is possible to engage for the first time N-aryl and N-benzyl imines in this cycloaddition reaction. A range of polysubstituted pyrrolidines is obtained with moderate to good yields and diastereoselectivities, using a simple palladium species (Pd(PPh3)4) and an archetypical phosphoric acid as catalyst combination. A two-step scheme which exploits the same palladium catalyst for two consecutive and mechanistically distinct reactions (the cycloaddition and a Suzuki–Miyaura cross-coupling) is also presented. This synergistic catalysis approach is well posited for the development of the enantioselective version of this reaction. A screening of common BINOL-derived chiral phosphoric acids as catalyst component identified a species giving the product with moderate, yet promising, enantioselectivity (64% ee).

Stereoselective Syntheses of Highly Functionalized Imidazolidines and Oxazolidines via Ring-Opening Cyclization of Activated Aziridines and Epoxides with Amines and Aldehydes

A mild one-pot stereospecific synthetic route to highly functionalized imidazolidines and oxazolidines via S_N2-type ring-opening of the corresponding activated aziridines and epoxides with amines followed by p-toluenesulfonic acid (PTSA)-catalyzed intramolecular cyclization with aldehydes has been developed. The methodology tolerates a variety of functional groups and furnishes the desired products in high yields (up to 92%) with excellent stereoselectivities (de, ee > 99%). Interestingly, imidazolidines were formed as the cis-isomers, whereas oxazolidines were produced as trans-isomers exclusively.

Enantioselective Mannich Reactions of 3-Fluorooxindoles with Cyclic N-Sulfamidate Aldimines

Both the 3-fluorooxindole and cyclic sulfamidate frameworks are important in medicinal chemistry owing to their associated biological activities. We report an approach accessing 3-fully substituted 3-fluorooxindoles, containing a benzo-fused sulfamidate subunit through highly enantioselective Mannich-type reactions between 3-fluorooxindoles and cyclic benzo-fused N-sulfamidate aldimines. These reactions are promoted by a commercially available cinchona alkaloid catalyst, accommodate a broad substrate scope, and deliver the desired products in a yield of up to 99% with an enantiomeric excess of up to 94%. A plausible reaction pathway is also presented.

Pd-Catalyzed diastereoselective [3 + 2] cycloaddition of vinylcyclopropanes with sulfamate-derived cyclic imines

The palladium-catalyzed diastereoselective [3 + 2] cycloaddition reaction of vinylcyclopropanes with sulfamate-derived cyclic imines worked efficiently under mild conditions, providing sulfamate-fused pyrrolidines in good to excellent yields.