Palladium‐Catalyzed Carbonylations of Aryl Bromides using Paraformaldehyde: Synthesis of Aldehydes and Esters

Carbonylation reactions represent useful tools for organic synthesis. However, the necessity to use gaseous carbon monoxide is a disadvantage for most organic chemists. To solve this problem, novel protocols have been developed for conducting palladium‐catalyzed reductive carbonylations of aryl bromides and alkoxycarbonylations using paraformaldehyde as an external CO source (CO gas free). Hence, aromatic aldehydes and esters were synthesized in moderate to good yields.     

Palladium‐Catalyzed Asymmetric Reductive Heck Reaction of Aryl Halides

Asymmetric reductive Heck reaction of aryl halides is realized in high stereoselectivity. Hydrogen‐bond donors, trialkylammonium salts in a glycol solvent, were used to promote halide dissociation from neutral arylpalladium complexes to access cationic, stereoselective pathways.     

Palladium‐Catalyzed Vicinal Amino Alcohols Synthesis from Allyl Amines by In Situ Tether Formation and Carboetherification

Vicinal amino alcohols are important structural motifs of bioactive compounds. Reported herein is an efficient method for their synthesis based on the palladium‐catalyzed oxy‐alkynylation, oxy‐arylation, or oxy‐vinylation of allylic amines. High regio‐ and stereoselectivity were ensured through the in situ formation of a hemiaminal tether using the cheap commercially available trifluoroacetaldehyde in its hemiacetal form. The obtained compounds are important building blocks, which can be orthogonally deprotected to give either free alcohols, amines, or terminal alkynes.     

Palladium(II)‐Catalyzed Synthesis of Sulfinates from Boronic Acids and DABSO: A Redox‐Neutral,Phosphine‐Free Transformation

A redox‐neutral palladium(II)‐catalyzed conversion of aryl, heteroaryl, and alkenyl boronic acids into sulfinate intermediates, and onwards to sulfones and sulfonamides, has been realized. A simple Pd(OAc)₂ catalyst, in combination with the sulfur dioxide surrogate 1,4‐diazabicyclo[2.2.2]octane bis(sulfur dioxide) (DABSO), is sufficient to achieve rapid and high‐yielding conversion of the boronic acids into the corresponding sulfinates. Addition of C‐ or N‐based electrophiles then allows conversion into sulfones and sulfonamides, respectively, in a one‐pot, two‐step process.     

Synthesis of Acylphosphonates by a Palladium‐Catalyzed Phosphonocarbonylation Reaction of Aryl Iodides with Phosphites

Acylphosphonates are conveniently synthesized from aryl iodides by a palladium‐catalyzed reaction with dialkyl phosphites under an atmospheric pressure of carbon monoxide. The reaction demonstrates the first example of the use of phosphorus nucleophiles in related metal‐catalyzed carbonylation reactions.     

Diaryl Sulfoxides from Aryl Benzyl Sulfoxides: A Single Palladium‐Catalyzed Triple Relay Process

A novel approach to produce diaryl sulfoxides from aryl benzyl sulfoxides is reported. Optimization of the reaction conditions was performed using high‐throughput experimentation techniques. The [Pd(dba)₂]/NiXantPhos catalyst system successfully promotes a triple relay process involving sulfoxide α‐arylation, C? S bond cleavage, and C? S bond formation. The byproduct benzophenone is formed by an additional palladium‐catalyzed process. It is noteworthy that palladium‐catalyzed benzylative C? S bond cleavage of sulfoxides is unprecedented. A wide range of aryl benzyl sulfoxides, as well as alkyl benzyl sulfoxides with various (hetero)aryl bromides were employed in the triple relay process in good to excellent yields (85–99 %). Moreover, aryl methyl sulfoxides, dibenzyl sulfoxides, and dimethylsulfoxide could be utilized to generate diaryl sulfoxides involving multiple catalytic cycles by a single catalyst.     

Palladium‐Catalyzed para‐Selective Alkylation of Electron‐Deficient Arenes

Intermolecular alkylations of electron‐deficient arenes proceed with good para selectivity. Palladium catalysts were used to generate nucleophilic alkyl radicals from alkyl halides, which then directly add onto the arenes. The arene scope and the site of alkylation are opposite to those of classical Friedel–Crafts alkylations, which prefer electron‐rich systems.     

The Ketene‐Surrogate Coupling: Catalytic Conversion of Aryl Iodides into Aryl Ketenes through Ynol Ethers

tert‐Butoxyacetylene is shown to undergo Sonogashira coupling with aryl iodides to yield aryl‐substituted tert‐butyl ynol ethers. These intermediates participate in a [1,5]‐hydride shift, which results in the extrusion of isobutylene and the generation of aryl ketenes. The ketenes are trapped in situ with multiple nucleophiles or undergo electrocyclic ring closure to yield hydroxynaphthalenes and quinolines.     

CO/C‐H as an Acylating Reagent: A Palladium‐Catalyzed Aerobic Oxidative Carbonylative Esterification of Alcohols

A palladium‐catalyzed oxidative carbonylative esterification of a variety of functionalized alcohols under base‐ and ligand‐free conditions has been demonstrated. A CO/olefin combination was utilized as the acylating reagent with O₂ as a benign oxidant. Notably, the scope of the substrate alcohols has been greatly broadened.     

Palladium‐Catalyzed Carbonylation Reactions of Aryl Halides and Related Compounds

A CO group richer : (Hetero)arenes are vital intermediates in the manufacture of agrochemicals, dyes, pharmaceuticals, and other industrial products. In the past decades transition‐metal‐catalyzed coupling reactions of aryl halides with all types of nucleophiles have been developed. This Review summarizes recent work in the area of palladium‐catalyzed carbonylation reactions of aryl halides and related compounds (see scheme).

     

Palladium‐Catalyzed Decarboxylative Cycloaddition of Vinylethylene Carbonates with Formaldehyde: Enantioselective Construction of Tertiary Vinylglycols

An efficient method for the enantioselective construction of tertiary vinylglycols through a palladium‐catalyzed asymmetric decarboxylative cycloaddition of vinylethylene carbonates with formaldehyde was developed. By using a palladium complex generated in situ from [Pd₂(dba)₃]?CHCl₃ and a phosphoramidite ligand as a catalyst under mild reaction conditions, the process allows conversion of racemic 4‐substituted 4‐vinyl‐1,3‐dioxolan‐2‐ones into the corresponding 1,3‐dioxolanes, as methylene acetal protected tertiary vinylglycols, in high yields with good to excellent enantioselectivities.