Asymmetric auto-tandem catalysis with a planar-chiral ruthenium complex: sequential allylic amidation and atom-transfer radical cyclization

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

Revisiting the 1,3-azadiene-succinic anhydride annulation reaction for the stereocontrolled synthesis of allylic 2-oxopyrrolidines bearing up to four contiguous stereocenters

Polysubstituted 2-oxopyrrolidines bearing at least two contiguous stereocenters constitute the core of several pharmaceuticals, including clausenamide (antidementia). Here, we describe a flexible annulation strategy, which unites succinic anhydride and 1,3-azadienes to produce allylic 2-oxopyrrolidines bearing contiguous stereocenters. The approach is chemoselective, efficient, modular, scalable, and diastereoselective. The scalable nature of the reactions offers the opportunity for post-diversification, leading to incorporation of motifs with either known pharmaceutical value or that permit subsequent conversion to medicinally relevant entities.

Molybdenum-Catalyzed Regio- and Enantioselective Amination of Allylic Carbonates: Total Synthesis of (S)-Clopidogrel

The first molybdenum-catalyzed highly regio- and enantioselective allylic amination of both aryl- and alkyl-substituted branched allylic carbonates has been developed. A wide variety of amines, including drugs and complex bioactive molecules, underwent successful amination with excellent reaction outcomes (up to 96% yield, >99% ee, and >20:1 b/l). The reaction could be scaled up and has been applied to the total synthesis of chiral drug molecule (S)-clopidogrel (Plavix).

Palladium(0) π-Lewis Base Catalysis: Concept and Development

The development of a new catalytic strategy plays a vital role in modern organic chemistry since it permits bond formation in an unprecedented and more efficient manner. Although the application of preformed metal complexes as π-base-activated reagents have enabled diverse transformations elegantly, the concept and strategy by directly utilizing transition metals as efficient π-Lewis base catalysts remain underdeveloped, especially in the field of asymmetric catalysis. Here, we outline our perspective on the discovery of palladium(0) as an efficient π-Lewis base catalyst, which is capable of increasing the highest occupied molecular orbital (HOMO) energy of both electron-neutral and electron-deficient 1,3-dienes and 1,3-enynes upon flexible η2-complexes formed in situ and resultant π-backdonation. Thus, fruitful carbon-carbon-forming reactions with diverse electrophiles can be achieved enantioselectively in a vinylogous addition pattern, which is conceptually different from the classical oxidative cyclization mechanism. Emphasis will be given to the concept and mechanism elucidation, catalytic features, and reaction design together with perspective on the further development of this emerging field.

Synthesis of Chiral Diarylmethylamides via Catalytic Asymmetric Aza-Michael Addition of Amides to ortho-Quinomethanes

Chiral diarylmethylamides are a privileged skeleton in many bioactive molecules. However, the enantioselective synthesis of such molecules remains a long-standing challenge in organic synthesis. Herein, we report a chiral bifunctional squaramide catalyzed asymmetric aza-Michael addition of amides to in situ generated ortho-quinomethanes, affording enantioenriched diarylmethylamides in good yields with excellent enantioselectivities. This work not only provides a new strategy for the construction of the diarylmethylamides but also represents the practicability of amides as nitrogen-nucleophiles in asymmetric organocatalysis.

Synthesis, stereochemical assignment, and enantioselective catalytic activity of late transition metal planar chiral complexes

Planar chirality is an important form of molecular chirality that can be utilized to induce enantioselectivity when incorporated into transition metal catalysts. However, due to synthetic constraints, the use of late transition metal planar chiral complexes to conduct enantioselective transformations has been limited. Additionally, the published methods surrounding the stereochemical assignment of planar chiral compounds are sometimes conflicting, making proper assignment difficult. This review aims to provide clarity on the methods available to assign planar chirality and provide an overview on the synthesis and use of late transition metal planar chiral complexes as enantioselective catalysts.

Diastereospecific arylation and cascade deconstructive amidation/thioesterification of readily available lactam-fused bromolactones

An intrinsic goal when designing synthetic methodology is to identify approaches whereby readily accessible precursors are converted into an array of products, which efficiently tap into new 3D-chemical space. In these studies, readily available bicyclic lactam-bromolactones have been interrogated in several fragment growth protocols by utilizing the halogen and lactone motifs as versatile linchpins for strategic construction of C-C, C-N, C-O, and C-S bonds. Diastereospecific C(sp3)-C(sp2) Kumada coupling of sterically imposing [5,5]-bicyclic lactam-bromolactones with several aryl Grignard reagents, under palladium catalysis, furnishes diarylmethane-tethered lactam-lactones in synthetically attractive yields, stereoinvertive fashion, and with a tolerance for many functional groups. When [5,6]-bicyclic lactam-bromolactones, which are prone to β-hydride elimination are employed, efficient arylation is observed only under Co(acac)3-catalyzed conditions. Importantly, these [5,6]-bicyclic lactam-bromolactones undergo retentive arylation, independent of the transition metal catalyst. A base-mediated cascade deconstructive amidation of the [5,6]-bicyclic lactam-bromolactones with primary aliphatic amines proceeds efficiently to afford epoxide-tethered lactam carboxamides, which bear four contiguous stereocenters. Furthermore, an unusual route to homoallylic thioesters has been uncovered through deconstructive contra-thermodynamic thioesterification of the lactam-fused bromolactone precursors.

Cu-Catalyzed Asymmetric Kinetic Boron Conjugate Addition of γ-Substituted α,β-Unsaturated γ-Lactams

Chiral α,β-unsaturated γ-lactams bearing simple γ- substituents are found in biologically active molecules and natural products, however, their synthesis still remains difficult. Herein, we report an efficient kinetic resolution (KR) of γ-substituted α,β-unsaturated γ-lactams via a Cu-catalyzed asymmetric boron conjugate addition, which also leads to the efficient synthesis of chiral β-hydroxy-γ-lactams with β,γ-stereogenic carbon centers. The KR proceeded smoothly with a wide range of γ-alkyl or aryl substituted substrates including those bearing aromatic heterocycles and different N-protected substrates in up to 347 of s value. Their highly versatile transformations, synthetic utility in biologically active molecules, and inhibitory activities against cisplatin-sensitive ovarian cancer cell A2780 have also been demonstrated. Differing from the well-known mechanism involving Cu-B species in Cu-catalyzed boron conjugate additions, our mechanistic studies using density functional theory (DFT) calculations and experiments indicate that a Lewis acid CuI -catalyzed mechanism is the likely pathway in the catalytic reaction.

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.

Asymmetric Auto-Tandem Palladium Catalysis for 2,4-Dienyl Carbonates: Ligand-Controlled Divergent Synthesis

Developing new asymmetric auto-tandem catalysis processes, especially in a divergent manner, is highly attractive but extremely challenging. Presented herein is a palladium-catalyzed auto-tandem reaction between 2,4-dienyl carbonates and o-TsNH arylimines or trifluoroacetophenones that proceeds through a consecutive N-allylation, vinylogous addition, π-σ-π isomerization, and another N-allylation sequence. Importantly, switchable diastereodivergent synthesis could be achieved by tuning the chiral bisphosphine ligands, which led to the construction of a broad spectrum of fused tetrahydroquinoline architectures with moderate to excellent enantioselectivity. Ligand control even enabled effective access to regiodivergent azetidine or chemodivergent β-H elimination with fair enantioselectivity, further showing the versatility of the current auto-tandem catalysis.

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.

Metal-Free Stereoselective Synthesis of (E)- and (Z)-N-Monosubstituted β-Aminoacrylates via Condensation Reactions of Carbamates

N-monosubstituted β-aminoacrylates are building blocks, which have been used in the preparation of amino acids and pharmaceuticals. Two efficient, stereoselective methods of preparation, via acid- or base-promoted condensation reactions of carbamates, are described. The base-promoted reaction is E-selective, while acid catalysis can, through the choice of solvent, selectively form E or Z. The acid-catalyzed E-selective process proceeds through a crystallization obviating the need for chromatographic purification.

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.

Pd-Catalyzed Rearrangement of N-Alloc-N-allyl Ynamides via Auto-Tandem Catalysis: Evidence for Reversible C-N Activation and Pd(0)-Accelerated Ketenimine Aza-Claisen Rearrangement

An auto-tandem catalytic double allylic rearrangement of N-alloc-N-allyl ynamides was developed. This reaction proceeds through two separate and distinct catalytic cycles with both decarboxylative Pd-π-allyl and Pd(0)-promoted aza-Claisen rearrangements occurring. A detailed mechanistic study supported by computations highlights these two separate mechanisms. Previously unreported reversible C-N ionization and a Pd(0)-catalyzed [3,3]-sigmatropic rearrangement were discovered. This study provides new reaction pathways for both π-allyl and sigmatropic rearrangements.

Al-thamili D, Almansour AI, Arumugam N, Dege N. [Bmim]Br Accelerated One-Pot Three-Component Cascade Protocol for the Construction of Spirooxindole-Pyrrolidine Heterocyclic Hybrids

Our synthetic approach for the assembly of structurally complex spirooxindole heterocyclic hybrids was based on an ionic liquid, [bmim]Br mediated one-pot three-component cascade reaction strategy involving 1,3-dipolar cycloaddition reaction of N-1-(2-pyridinylmethyl)-3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones and azomethine ylide generated in situ from isatin and L-phenyl alanine, affording a series of spirooxindole-pyrrolidine heterocyclic hybrids in good-to-excellent yields. In addition to serving as the reaction medium, [bmim]Br also functioned as a catalyst in this cycloaddition reaction and hence accelerated the reaction rate affording the cycloadducts in short reaction time.

Ruthenium-Catalyzed Asymmetric Allylic Alkylation of Isatins

A new ruthenium-based catalytic system for branched-selective asymmetric allylic alkylation is disclosed and applied to the synthesis of chiral isatin derivatives. The catalyst, which is generated in situ from commercially available CpRu(MeCN)₃PF₆ and a BINOL-derived phosphoramidite, is both highly active (TON up to 180) and insensitive to air and moisture. Additionally, the N-alkylated isatins accessible using this methodology are versatile building blocks that are readily transformed into chiral analogs of achiral drug molecules.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

Synthesis of an optically active polymer containing a planar phthalimide backbone by asymmetric polymerization

Herein we present the precise design and synthesis of a novel polymer backbone that induces a helical structure through asymmetric polymerization reactions of a phthalimide-based monomer catalyzed by a planar-chiral cyclopentadienyl–ruthenium complex.

Side-Chain-Driven Dual Structural System of Poly-Arylopeptide: Selective Helical Formation Derived from Aromatic Ring Flips on the Backbone

A methodology for producing dual structural systems of macromolecules, which involves flipping the unsymmetrical aromatic rings on the main chain is presented. Previously, we reported a non-natural polypeptide containing an aromatic ring on the peptide backbone, called a poly "arylopeptide". Herein, we used 2,6-naphthalene rings as axially unsymmetrical spacers, which has two geometrical isomers, anti and syn, to create dual structural properties. The miniscule energy difference between the two geometrical isomers can be amplified by incorporating the 2,6-naphthylene units into the polypeptide backbone, which creates a thermodynamic driving force for the formation of two specific global structures (i.e., 3₁-helix or 4₁-helix) biased toward one side geometrical isomer depending on the side chain. Additionally, the 3₁-helix can be switched to the 4₁-helix upon addition of a small amount of additives, indicating a conformational conversion from an identical sequence. The developmental dual helical systems exploit basic molecular geometry and can serve as a design platform for synthetic polymers.

Rh(III)-Catalyzed Annulation of Boc-Protected Benzamides with Diazo Compounds: Approach to Isocoumarins

A mild rhodium-catalyzed annulation of Boc-protected benzamides with diazo compounds via C−C/C−O bond formation has been explored. In the presence of [Cp*RhCl₂]₂, AgSbF₆ and Cs₂CO₃, Boc-protected benzamides can be effectively annulated to yield isocoumarins in 0.5–2 h.

α-Halogenoacetamides: versatile and efficient tools for the synthesis of complex aza-heterocycles

This review presents the use of α-alkyl- and α-alkoxy-halogenoacetamides as powerful partners for domino and 1,3-dipolar cycloaddition reactions resulting in a ring closure.