Nucleophilic Dearomatization of Chloromethyl Naphthalene Derivatives via η3-Benzylpalladium Intermediates: A New Strategy for Catalytic Dearomatization

Pd-Catalyzed Intramolecular Dearomative [4 + 2] Cycloaddition of Naphthalenes with Arylalkynes

A Pd-catalyzed intramolecular dearomative [4 + 2] cycloaddition reaction of naphthalenes with arylalkynes is developed. The protocol provides a straightforward method to access a range of polycyclic dihydronaphthalenes containing two vicinal all-carbon stereocenters in moderate yields under mild conditions in an air atmosphere. The deuterium labeling experiment suggests a pathway involving electrophilic dearomatization followed by Friedel-Crafts cyclization. Several synthetic transformations of the product were conducted to demonstrate the utility of this reaction.

Palladium-Catalyzed Para-C-H Bond Amination of 2-Aryl Chloromethylbenzenes

Palladium-catalyzed para-C-H bond amination of 2-aryl chloromethylbenzenes is described for the first time. The reactions of 2-aryl chloromethylbenzenes with cyclic amines proceeded smoothly in the presence of Pd(acac)₂, tri(2-furyl)phosphine, and NaH in tetrahydrofuran at 40 °C to provide para-C-H bond aminated products in satisfactory to high yields with acceptable regioselectivity in most cases. The electronic property of the substituents linked to the benzene rings did not significantly influence the reactivity of the 2-aryl chloromethylbenzene substrates and the reaction regioselectivity.

Confronting the Challenging Asymmetric Carbonyl 1,2-Addition Using Vinyl Heteroarene Pronucleophiles: Ligand-Controlled Regiodivergent Processes through a Dearomatized Allyl-Cu Species

The selective reductive coupling of vinyl heteroarenes with aldehydes and ketones represents a versatile approach for the rapid construction of enantiomerically enriched secondary and tertiary alcohols, respectively. Herein, we demonstrate a CuH-catalyzed regiodivergent coupling of vinyl heteroarenes with carbonyl-containing electrophiles, in which the selectivity is controlled by the ancillary ligand. This approach leverages an in situ generated benzyl- or dearomatized allyl-Cu intermediate, yielding either the dearomatized or exocyclic addition products, respectively. The method exhibits excellent regio-, diastereo-, and enantioselectivity and tolerates a range of common functional groups and heterocycles. The dearomative pathway allows direct access to a variety of functionalized saturated heterocyclic structures. The reaction mechanism was probed using a combination of experimental and computational approach. Density functional theory studies suggest that the ligand-controlled regioselectivity results from the C-H/π interaction and steric repulsion in transition states, leading to the major and minor regioisomers, respectively. Hydrocupration of vinyl heteroarene pronucleophile is the enantiodetermining step, whereas the diastereoselectivity is enforced by steric interactions between the benzylic or allyl-Cu intermediate and carbonyl-containing substrates in a six-membered cyclic transition state.

Pd-catalyzed allylative dearomatisation using Grignard reagents

Pd-catalyzed allylative dearomatisation of naphthyl halides is shown to be feasible by employing Grignard reagents. The high reactivity of the nucleophile allows for fast reactions and low catalyst loading, while a plethora of successfully substituted compounds illustrate the broad scope. Five membered heteroaromatic compounds are also demonstrated to be reactive under similar conditions.

Highly Regioselective Aromatic C-H Allylation of N-(Arylmethyl)sulfonimides with Allyl Grignard Reagents Involving Benzylic C-N Cleavage

A new pair of reaction partners has been established for the aromatic C-H functionalization of benzyl electrophiles with nucleophiles via palladium-catalyzed benzylic C-N cleavage. A range of N-(1-naphthylmethyl)sulfonimides, N-(2-thienylmethyl)sulfonimides, and N-(2-furanylmethyl)sulfonimides smoothly underwent palladium-catalyzed aromatic C-H allylation with allyl Grignard reagents at room temperature, delivering structurally diverse substituted 1-allylnaphthalenes and 2-allylheteroarenes in moderate to excellent yields with extremely high regioselectivities. Replacing the N-(arylmethyl)sulfonimide with an (arylmethyl)ammonium salt, an arylmethyl chloride, or an arylmethyl phosphate as the benzyl electrophile leads to a dramatic erosion of the regioselectivity.

Platinum-Catalyzed Intramolecular Spirocyclization of N-(Methylnaphthalenyl)propiolamides via Formal Aromatic Ene Reaction

It has been established that an in situ-generated cationic platinum(II)/rac-BINAP complex catalyzes the intramolecular dearomative 5-endo spirocyclization of N-(methylnaphthalenyl)propiolamides via the deprotonation-protonation sequence (formal aromatic ene reaction). Mechanistic studies revealed that our previously reported dearomative 6-endo cyclization followed by the Friedel-Crafts reaction is kinetically and thermodynamically unfavored, and thus, the 5-endo spirocyclization proceeds selectively.

Catalytic three-component C-C bond forming dearomatization of bromoarenes with malonates and diazo compounds

A Pd-catalyzed dearomative three-component C-C bond formation of bromoarenes with diazo compounds and malonates was developed. Various bromoarenes ranging from benzenoids to azines and heteroles were transformed to the corresponding substituted alicyclic molecules. The key to this reaction is the generation of a benzyl-palladium intermediate, which reacts with malonates to form a Pd-O-enolate species. Strikingly, the present method enabled rapid access to multi-substituted alicycles through subsequent elaboration of dearomatized products.

Palladium-catalyzed dearomative 1,4-difunctionalization of naphthalenes

A highly diastereoselective dearomatization of naphthalenes via a Pd-catalyzed 1,4-difunctionalization reaction is described. In the presence of a commercially available palladium precursor and ligand, intramolecular dearomative Heck-type insertion provides π-allylpalladium intermediates which are readily captured by a series of nucleophiles in excellent yields (up to 99%). This reaction features mild conditions, broad substrate scope, and useful transformations of the products.

Connecting remote C-H bond functionalization and decarboxylative coupling using simple amines

Transition metal-catalyzed C–H functionalization and decarboxylative coupling are two of the most notable synthetic strategies developed in the last 30 years. Herein, we connect these two reaction pathways using bases and a simple Pd-based catalyst system to promote a para-selective C–H functionalization reaction from benzylic electrophiles. Experimental and computational mechanistic studies suggest a pathway involving an uncommon Pd-catalyzed dearomatization of the benzyl moiety followed by a base-enabled rearomatization through a formal 1,5-hydrogen migration. This reaction complements “C–H activation” strategies that convert inert C–H bonds into C–metal bonds prior to C–C bond formation. Instead, this reaction exploits an inverted sequence and promotes C–C bond formation prior to deprotonation. These studies provide an opportunity to develop general para-selective C–H functionalization reactions from benzylic electrophiles and show how new reactive modalities may be accessed with careful control of reaction conditions.

Palladium-Catalyzed Dearomative syn-1,4-Carboamination with Grignard Reagents

A protocol for palladium-catalyzed dearomative functionalization of simple, nonactivated arenes with Grignard reagents has been established. This one-pot method features a visible-light-mediated [4+2] cycloaddition between an arene and an arenophile, and subsequent palladium-catalyzed allylic substitution of the resulting cycloadduct with a Grignard reagent. A variety of arenes and Grignard reagents can participate in this process, forming carboaminated products with exclusive syn-1,4-selectivity. Moreover, the dearomatized products are amenable to further elaborations, providing functionalized alicyclic motifs and pharmacophores. For example, naphthalene was converted into sertraline, one of the most prescribed antidepressants, in only four operations. Finally, this process could also be conducted in an enantioselective fashion, as demonstrated with the desymmetrization of naphthalene.

Palladium-Catalyzed Ligand-Controlled Regioselective Nucleophilic Aromatic Substitution of 1-(Chloromethyl)naphthalenes with Arylacetonitriles

The palladium-catalyzed reaction of 1-(chloromethyl)naphthalenes 1 with (hetero)arylacetonitriles 2 gives either para- or ortho-acylated naphthalenes (3 or 4) in good to high yields. The regioselectivity can be controlled by the ligand of a palladium catalyst. A sterically bulky ligand, ^tBuPPh₂, affords para-acylated products 3, whereas a sterically less bulky ligand, Me₂PPh, provides ortho-acylated products 4. Further, direct substitution product 5 at the benzylic position is not obtained essentially, although such a reaction at the benzylic position is favorable in ordinary nucleophilic substitutions. In this paper, it was revealed that the benzylpalladium intermediate could react through a different mode (η³-benzylpalladium intermediate or η¹-benzylpalladium intermediate) in nucleophilic aromatic substitution. In addition to the interesting mechanistic aspect, the present reaction provides a facile synthetic method for a wide range of diaryl ketones, some of which are not easily available through the previously known procedures.

Recent advances in chemical dearomatization of nonactivated arenes

Dearomatization reactions provide a synthetic connection between readily available, simple aromatic starting materials and more saturated intermediates of greater molecular complexity and synthetic utility. The last decade has witnessed a steady increase in the development of dearomative methods, providing new synthetic approaches to high-value building blocks and natural products. This review highlights advances both in the area of dearomatization methodologies for the most chemically inert arenes and in synthetic applications of such strategies.

Stille cross-coupling of secondary and tertiary α-(trifluoromethyl)-benzyl chlorides with allylstannanes

A Stille cross-coupling reaction was developed for the first time by secondary (trifluoromethyl)benzyl chlorides and allylstannanes.

Palladium-Catalyzed Asymmetric Benzylic Substitution of Secondary Benzyl Carbonates with Nitrogen and Oxygen Nucleophiles

A Pd/(R)-BINAP-catalyzed asymmetric benzylic substitution of secondary benzyl carbonates with amides and amines proceeds to form the corresponding optically active benzylamines in good yields with a high enantiomeric ratio. The reaction occurs in a dynamic kinetic asymmetric transformation (DYKAT) manner. Additionally, the asymmetric Pd catalysis can also be applicable to phenol nucleophiles, thus delivering chiral ethers with acceptable yields and enantioselectivity.

Palladium-catalyzed reductive Heck-type vinylative dearomatization of unfunctionalized halonaphthalene derivatives

A novel strategy for the dearomatization of inactive 1-halonaphthalenes via palladium-catalyzed reductive Heck-type vinylative reaction was successfully developed.

Decarboxylative dearomatization and mono-α-arylation of ketones

Ligand-controlled decarboxylative coupling of benzyl enol carbonates provides dearomatized products via enantiospecific coupling or alpha-aromatic ketones via dearomatization–rearomatization.

Mercaptobenzoic acid-palladium(0) complexes as active catalysts for S-benzylation with benzylic alcohols via (η3-benzyl)palladium(ii) cations in water

Mercaptobenzoic acid-palladium(0) complexes show high catalytic activity for S-benzylation with benzylic alcohols via the (η³-benzyl)palladium(ii) cation in water. The catalytic system can be performed using only 2.5 mol% Pd₂(dba)₃ without the phosphine ligand or other additives.

Regio- and chemoselective palladium-catalyzed benzylallylation of activated olefins: the remarkable effect of palladium nanoparticles

The palladium-catalyzed three-component reactions of benzyl halides, activated olefins, and allyltributylstannane were successfully conducted to produce the corresponding benzylallylation products in satisfactory to high yields. The benzylallylation reaction proceeded smoothly under mild conditions in the presence of palladium nanoparticles in tetrahydrofuran.

Palladium-catalyzed, pyrrolidine-mediated arylmethylation of ketones and aldehydes with coumarinyl(methyl) acetates

We report the palladium-catalyzed, pyrrolidine-mediated α-benzylation of enamines generated from aldehydes and ketones. The method allows for direct coupling of medicinally relevant coumarin moieties with aldehydes and ketones in good yield under mild conditions. The reaction is believed to proceed via a Pd-π-benzyl complex generated from (coumarinyl)methyl acetates.