Palladium-Catalyzed Heck-type Domino Cyclization and Carboxylation to Synthesize Carboxylic Acids by Utilizing Chloroform as the Carbon Monoxide Source

Pd-Catalyzed Cascade Cyclization/Thiocarbonylation with Thioformates: Synthesis of Thioester-Functionalized Oxindoles

A Pd-catalyzed thiocarbonylative cyclization of N-(o-iodoaryl)acrylamides with easily accessible thioformates has been developed. The reaction has a wide substrate scope with good yields and represents a powerful route to the synthesis of thioester-functionalized oxindoles. Both S-aryl and alkyl thioformates as the thioester sources were well tolerated. The active Pd-CO intermediate may play an important role in the transformation process.

Enantioselective Palladium-Catalyzed Domino Carbonylative Heck Esterification of o-Iodoalkenylbenzenes with Arylboronic Acids

The current investigation presents an innovative palladium-catalyzed asymmetric carbonylative Heck esterification method. This approach facilitates the efficient synthesis of various chiral γ-ketoacid esters by utilizing o-alkenyliodobenzenes and arylboronic acids as primary substrates. This reaction achieves the creation of three carbon-carbon bonds, two carbon-oxygen bonds, and the establishment of a quaternary carbon center within a single step. The α-chiral γ-ketoacid esters were obtained in yields ranging from good to high yields, displaying enantiomeric excesses (ee's) levels up to 92% under mild reaction conditions.

Photochemically induced chloromethylation/cyclization of benzimidazole derivatives with CCl4/CHCl3

Herein, it is reported that a series of trichloromethyl/dichloromethyl substituted benzimidazole derivatives have been synthesized by dechlorination of CCl4/CHCl3 to form polychloromethyl radicals and cyclization with an unactivated olefin under a purple LED lamp. The protocol features a wide substrate scope, high atom economy, and excellent regioselectivity, and is easy to scale up.

Palladium-catalyzed Heck-carbonylation of alkene-tethered carbamoyl chlorides with aryl formates

We report a palladium-catalyzed Heck-carbonylation of alkene-tethered carbamoyl chlorides by utilizing aryl formates as convenient CO surrogates. One C-O and two C-C bonds are constructed to give diversiform esterified oxindoles/γ-lactams bearing an all-carbon quaternary stereocenter under gas-free conditions. This transformation features a wide substrate scope and good functional group tolerance and can be easily applied to late-stage functionalization.

Palladium-Catalyzed Heck Cyclization with P(O)H Compounds to Construct Phosphinonyl-Azaindoline and -Azaoxindole Derivatives

We report herein a concise method for the construction of phosphinonyl-azaindoline and -azaoxindole derivatives via a palladium-catalyzed cascade cyclization with P(O)H compounds. Various H-phosphonates, H-phosphinates, and aromatic secondary phosphine oxides are all tolerated under the reaction conditions. Furthermore, the phosphinonyl-azaindoline isomer families such as 7-, 5-, and 4-azaindolines could be synthesized in moderate to good yields.

Palladium-Catalyzed Aminocarbonylation of Isoquinolines Utilizing Chloroform-COware Chemistry

The carbonyl group forms an integral part of several drug molecules and materials; hence, synthesis of carbonylated compounds remains an intriguing area of research for synthetic and medicinal chemists. Handling toxic CO gas has several limitations; thus, using safe and effective techniques for in or ex situ generation of carbon monoxide from nontoxic and cheap precursors is highly desirable. Among several precursors that have been explored for the generation of CO gas, chloroform can prove to be a promising CO surrogate due to its cost-effectiveness and ready availability. However, the one-pot chloroform-based carbonylation reaction requires strong basic conditions for hydrolysis of chloroform that may affect functional group tolerability of substrates and scale-up reactions. These limitations can be overcome by a two-chamber reactor (COware) that can be utilized for ex situ CO generation through hydrolysis of chloroform in one chamber and facilitating safe carbonylation reactions in another chamber under mild conditions. The versatility of this "Chloroform-COware" technique is explored through palladium-catalyzed aminocarbonylation of medicinally relevant heterocyclic cores, viz., isoquinoline and quinoline.

Highly Diastereoselective Synthesis of Oxindoles Containing Vicinal Quaternary and Tertiary Stereocenters by a Domino Heck/Decarboxylative Alkynylation Sequence

A palladium-catalyzed domino Heck/decarboxylative alkynylation reaction of trisubstituted alkenes or enamines is reported. For two different types of substrates, the current domino reaction employing different solvents and bases led to 3,3-disubstituted oxindoles and hydropyrimidinyl spirooxindoles containing vicinal quaternary and tertiary stereocenters in moderate to good yields, respectively. The general applicability of this method was shown by gram-scale syntheses and diverse transformations of the reaction products. The enantioselective version for this domino process was also studied.

Palladium-Catalyzed Aminocarbonylation of (Hetero)aryl Iodides with α-Amino Acid Esters as Nucleophiles

We report palladium-catalyzed aminocarbonylation of (hetero)aryl iodides with α-amino acid esters as nucleophiles. The synthesized N-capped α-amino acids are biologically important building blocks. The mild conditions provide products with high enantioselectivity at 80 °C in 35 min. The reactions are performed under air in a sealed vessel using chloroform as an in situ CO source. For the first time, regioselective carbonylation of histidine is also presented.

Palladium-catalyzed Heck cyclization/allylation with homoallyl alcohols via retro-allylation

A palladium-catalyzed reaction of aryl iodide-tethered alkenes with homoallyl alcohols is reported, providing a convenient and efficient approach to C(sp3)–allylation products.

Palladium-Catalyzed Aryl-Furanylation of Alkenes: Synthesis of Benzofuran-Containing 3,3-Disubstituted Oxindoles

A novel palladium-catalyzed aryl-furanylation of alkenes is described. This protocol provided a straightforward route to the synthesis of various benzofuran-containing 3,3-disubstitutedoxindole derivatives bearing a quarternary carbon center. In the cascade process, one C(sp²)-O bond, two C(sp²)-C(sp³) bonds, an oxindole, and a furan ring are formed in a single chemical operation.

Palladium Nanoparticles Anchored on Magnesium Organosilicate: An Effective and Selective Catalyst for the Heck Reaction

A new and effective palladium catalyst supported on a magnesium organosilicate for application in the Heck reaction is presented. A group of compounds comprising 22 examples were synthesized in moderate to high yields (up to 99%) within a short time. The palladium supported on magnesium organosilicate catalyst was characterized as an amorphous solid by SEM, containing around 33% of palladium inside the solid, and even with this low quantity of palladium, the catalyst was very efficient in the Heck reaction. Besides, based on the Scherrer equation, the crystallite size of the synthesized palladium nanoparticles was ultrasmall (around 1.3 nm). This strategy is a simple and efficient route for the formation of C–C bonds via the Heck cross-coupling reaction.

Selective synthesis of acylated caprolactam via sequential Michael addition/palladium-catalyzed alpha-arylation of ketones

A formal [6 + 1] annulation reaction provides an efficient route enabling rapid access to diverse caprolactams by the double C–C bond formation of the same site from methyl ketones.

Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

A variety of chromone fused cyclopentanones are efficiently generated in good to high yields via palladium-catalyzed [2 + 2 + 1] annulation, in which cyclopropenone was utilized for the first time as the sole CO surrogate in the carbonylation process.

POP-Pd(ii) catalyzed easy and safe in situ carbonylation towards the synthesis of α-ketoamides from secondary cyclic amines utilizing CHCl3 as a carbon monoxide surrogate

POP-palladium(ii) was synthesized for the in situ carbonylation of aryl iodides and secondary cyclic amine to the respective α-ketoamides.

Chloroform as a CO surrogate: applications and recent developments

The carbonyl moiety is one of the indispensable sub-units in organic synthesis with significant applications in medicinal as well as materials chemistry. Hence the insertion of a carbonyl group via simple and highly efficient routes has been one of the most challenging tasks for organic chemists. Though the direct utilisation of CO gas in carbonylation is the fundamental procedure for the construction of carbonyl compounds, it has certain drawbacks due to its toxic and explosive nature. As a result, the need for cheap and efficient CO surrogates has gained much attention nowadays by which CO gas can be easily generated in situ or ex situ. In this review we discuss the advantages of chloroform as CO surrogate and have surveyed recent carbonylation reactions where chloroform has been used as CO source.

Chloroform as a carbon monoxide source in palladium-catalyzed synthesis of 2-amidoimidazo[1,2-a]pyridines

A palladium-catalyzed aminocarbonylation strategy exploiting chloroform as a CO source has been developed for the synthesis of biologically potent 2-amidoimidazopyridine scaffolds. The aminocarbonylation reaction was found to be general with a range of amines and substituted imidazopyridines. Preliminary biological evaluation of cytotoxicity on selected examples provides scope for future investigations.

ATRA-like alkylation–peroxidation of alkenes with trichloromethyl derivatives by the combination of tBuOOH and NEt3

This protocol provides a unique and innovative approach to the construction of α-tert-butylperoxy-β-dichloromethyl alkanes, employing CHCl₃ as an alkylating reagent to provide a –CHCl₂ group, and TBHP as an oxidant to provide an α-^tBuOO group.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

Easily fabricated and recyclable Pd&Cu@Al catalyst for gram-scale phosphine-free Heck reactions with high TON

A unique Pd&Cu@Al catalyst was easily fabricated just by immersing commercial aluminum foil in a mixed xylene solution of PdCl₂ and CuCl₂. The catalyst fabrication process led to aluminum oxide coatings in situ, which supported the metal nanoparticles and enhanced their catalytic activities for the phosphine-free Heck reaction of aryl halides and styrenes with high turnover number (TON) up to 3.9×10⁵. The reaction can be scaled up to at least 100mmol and has been applied in modification of drug Lapatinib's intermediate with low metal residue. This novel catalyst is of good application potential in industrial production because it was extremely easy to be recycled, in regardless of the generation of the insoluble impurities or tars during the reaction processes.

An effective Pd nanocatalyst in aqueous media: stilbene synthesis by Mizoroki-Heck coupling reaction under microwave irradiation

Aqueous Mizoroki–Heck coupling reactions under microwave irradiation (MW) were carried out with a colloidal Pd nanocatalyst stabilized with poly(N-vinylpyrrolidone) (PVP). Many stilbenes and novel heterostilbenes were achieved in good to excellent yields starting from aryl bromides and different olefins. The reaction was carried out in a short reaction time and with low catalyst loading, leading to high turnover frequency (TOFs of the order of 100 h⁻¹). The advantages like operational simplicity, high robustness, efficiency and turnover frequency, the utilization of aqueous media and simple product work-up make this protocol a great option for stilbene syntheses by Mizoroki–Heck reaction.

Thiocarbonyl Surrogate via Combination of Sulfur and Chloroform for Thiocarbamide and Oxazolidinethione Construction

An efficient and practical thiocarbonyl surrogate via combination of sulfur and chloroform has been developed. A variety of thiocarbamides and oxazolidinethiones have been established, including chiral thiourea catalysts and chiral oxazolidinethione auxiliaries with high selectivity. Meanwhile, pesticides Diafenthiuron (an acaricide), ANTU (a rodenticide), and Chloromethiuron (an insecticide) were practically synthesized through this method in gram scale. Dicholorocarbene, as the key intermediate, was further confirmed via a carbene-trapping control experiment.

Palladium-catalyzed aminocarbonylation of halo-substituted 7-azaindoles and other heteroarenes using chloroform as a carbon monoxide source

A palladium-catalyzed aminocarbonylation of halo-substituted 7-azaindoles and other heterocycles utilizing CHCl₃ as the carbonyl source has been developed for the straightforward incorporation of an amide functional group.

Oxalic acid as the in situ carbon monoxide generator in palladium-catalyzed hydroxycarbonylation of arylhalides

Oxalic acid as a highly efficient, safe and tractable concentrated carbon monoxide surrogate was successfully introduced into the palladium-catalyzed hydroxycarbonylation of arylhalides.

Heck Reactions Catalyzed by Ultrasmall and Uniform Pd Nanoparticles Supported on Polyaniline

Using air as the oxidant instead of the traditionally employed persulfates, the smaller and more uniform Pd nanoparticles (around 2 nm) supported on polyaniline (Pd@PANI) can be easily fabricated by the oxidation-polymerization of aniline with PdCl2. This material is an efficient and environmentally friendly catalyst for Heck reactions due to its recyclability, low loading, and ligand-free and mild reaction conditions. It was even tolerant to sulfur-containing substrates. This work reports the Pd@PANI-catalyzed Heck reactions with very wide substrate scopes, and discloses the catalytic mechanisms based on experimental findings and results of catalyst analysis and characterization.