Platinum pincer complexes featuring an SCS indenediide backbone have been prepared and evaluated in the catalytic cycloisomerization of alkynoic acids and N‐tosyl alkynylamides. One of the platinum complexes significantly outperforms its palladium analogue for the formation of 6‐ and 7‐membered rings. The catalytic system takes advantage of the alkynophilicity of Pt and of the non‐innocent character of the indenediide framework. Like for Pd, the catalytic performance is significantly improved by using an H‐bond donor additive such as pyrogallol. For the first time, a large variety of ω‐unsaturated δ‐ and ε‐lactones/lactams could be prepared with high selectivities and in very good yields.
The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.
The palladium‐catalysed dehydrogenation of sp3 carbon‐hydrogen bonds of N‐alkylbenzenesulfonamides allows a simple access to N‐alkenylbenzenesulfonamides. The reaction proceeds with easily accessible catalysts, with pivalate as a base, and allows a variety of substituents both on nitrogen and on the arene moiety.
An unprecedented stereospecific allylation reaction of nitroacetates with enantioenriched primary allylic amines has been developed. A range of nitroacetates smoothly underwent allylation with enantioenriched primary allylic amines in the presence of a palladium catalyst and boric acid followed by one‐pot decarboxylation to afford structurally diverse homoallylic nitro compounds in good to excellent yields with excellent retention of configuration. On the other hand, the allylation followed by denitronation provided a facile synthetic route to optically active β‐chiral γ,δ‐unsaturated esters.
Dehydrogenative coupling of primary alcohols with secondary amines to form tertiary amides and dihydrogen (H2) is efficiently catalyzed by bipyridyl‐based ruthenium pincer complexes (0.2–1 mol%) under neutral conditions (in case of the dearomatized complexes), or with added catalytic amount of base. The reaction is sensitive to steric hindrance; in the case of amidation of bulky secondary amines a less sterically hindered complex is more efficient. Selective acylation of primary amines in the presence of secondary amines was also demonstrated.
A novel and convenient palladium‐catalyzed cross‐coupling reaction of H‐phosphonate diesters with sodium arylsulfinates was developed via desulfitation in the presence of silver carbonate and tetra‐butylammonium chloride. This method is highly efficient and provides a rapid access to a broad spectrum of arylphosphonate diesters in good to excellent yields.
Silver‐catalyzed three‐component, tandem reactions of 4‐alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes, amines and various nucleophiles result in the formation of highly functionalized chromeno[3,4‐c]pyridin‐5‐ones in high yields. Gold‐catalyzed [4+2] cycloadditions of 4‐alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes with alkynes or alkenes have also been achieved to afford benzo[c]chromen‐6‐ones efficiently.
Cyclometallated NHC palladium complexes prepared from palladium(II) acetate [Pd(OAc)2] and unsymmetrical 1,3‐diarylimidazolinium salts catalyzed the hydroxymethylation of (hetero)arylboronic acids using an excess amount of formalin to afford (hetero)arylmethanols in good to satisfactory yields.
α‐Allenols were catalytically transformed into dihydrofurans in the presence of platinum dichloride. Notably, using platinum dichloride along with silver triflate as the catalytic system, α,β‐unsaturated ketones were obtained. Therefore, the role of the silver salt may not just consist in the activation of the platinum precatalyst.
A method for using amine–borane complexes directly in palladium catalyzed borylation has been developed. The reaction proceeds through the sequential formation of a boronium species followed by deprotonation leading to the aminoborane. This reagent is then directly used in the borylation process leading, after work‐up, to various boronic acid derivatives. The reaction was applied to (hetero)aryl triflates, iodides, bromides and chlorides.
A safe, facile and low‐leaching (up to 0.04 ppm) method has been developed for the removal of allyl, prenyl and benzyl protecting groups from the corresponding esters, using a sulfur‐modified gold‐supported palladium (SAPd) nanoparticle catalyst, which is known to be non‐flammable. The catalyst itself was found to be recyclable and the reaction appeared to proceed on the surface of the SAPd.
A one‐pot, two‐step cyclization reaction of iodoarenes with diversified arylols, including 4‐hydroxyquinoline, quinolinone, 4‐hydroxypyridine and phenol, has been developed. By using this palladium‐catalyzed formal tandem O‐arylation, dehydrogenative cross‐coupling reaction, a variety of biologically significant fused benzo[4,5]furo heterocycles and dibenzofurans were quickly assembled in high yields with excellent regioselectivity. Notably, the efficient one‐pot reaction led to the heterocycles via sequential oxidation, iodination, isomerization and cyclization steps without purification of any reaction intermediates.
We disclose the highly diastereoselective combination of monoamine oxidase‐catalyzed oxidation of meso‐pyrrolidines and aza‐Friedel–Crafts reactions in aqueous buffer to give valuable enantioenriched 2‐substituted pyrrolidines in a formal double C H activation process. A range of secondary as well as tertiary amines were shown to be suitable substrates for the biocatalytic oxidation and subsequent addition of a variety of C‐nucleophiles.
An efficient palladium(II)‐catalyzed method for the synthesis of alkylated pyridine‐substituted pyrroles has been developed by a one‐pot three component reaction of β‐bromovinyl aldehydes, primary amines and 2‐alkynylpyridines in good yields. The reactions can also provide an efficient route to 2‐picolinoylpyrroles by slightly altering the reaction conditions.
The N‐heterocyclic carbene (NHC)‐catalyzed oxidative amidation of aromatic aldehydes with amines in the presence of N‐bromosuccinimide (NBS) as an oxidant has been developed for the synthesis of amides. This amidation strategy is tolerant to both the electronic and the steric nature of the aryl aldehydes employed. The present methodology was extended to chiral amino acid derivatives to generate the corresponding amides in good yields and excellent ee values (>98%).
The three‐component reaction of α‐halomethyl oxime ethers, boronic acids and carbon monoxide at atmospheric pressure catalyzed by tetrakis(triphenylphosphine)palladium(0) gives efficiently unsymmetrical β‐alkoxyimino carbonyl compounds with total control of the regioselectivity, in high yield and atomic economy. Simple commercially available starting materials are used in this synthetic procedure. The three components assembly takes place preferentially versus the competing direct coupling or other possible side reactions. The mechanism of the transformation was investigated by NMR and intermediate palladium(II) complexes were detected.
