Pd(0)-catalyzed cross-coupling reactions of boron derivatives with a lactam-derived N-Boc enol triflate

[formula: see text] The cross-coupling reaction of 2-(1-alkenyl)-1,3,2-benzodioxaboroles, obtained from alkynes and catecholborane, and other boron derivatives with a lactam-derived N-Boc enol triflate occurred under very mild conditions in a THF-water medium employing (Ph3P)2PdCl2 as a catalyst, providing the corresponding 6-substituted N-Boc 3,4-dihydro-2H-pyridines in high yields.     

Microwave- and ultrasound-assisted Suzuki–Miyaura cross-coupling reactions catalyzed by Pd/PVP

Suzuki–Miyaura reactions using Pd/PVP as a catalyst source were carried out in water–ethanol solution. Under MW, sonication or thermal condition yields were very similar, from moderate to very good, in a variety of examples. However, TOFs were very different, 750/h under MW, 250/h under sonication, and 28/h under thermal conditions. Studies carried out under sonication showed that the whole system after product extraction can be re-used at least twice without any noticeable loss of yield.     

Heterogeneous Suzuki reactions catalyzed by Pd(0)-Y zeolite

The Pd(0)-Y zeolite showed high activity in the Suzuki cross-coupling reactions of aryl bromides without added ligands. The type of base and organic solvent were found to be critical for the efficiency of the reaction. The presence of water was essential within the reaction medium. The coupling reactions occurred on the external surface of the zeolite. The catalyst is reusable.     

Pd(DIPHOS)2-catalyzed cross-coupling reactions of organoborons with free or polymer-bound aryl halides

Bis[1,2-bis(diphenylphosphino)ethane]palladium(0) [Pd(DIPHOS)2] catalyzes cross-coupling reactions of free or polymer-bound aryl halides with organoboron compounds to produce biaryls in overall yields of 60-96%.     

Alkoxy- and amidocarbonylation of functionalised aryl and heteroaryl halides catalysed by a Bedford palladacycle and dppf: a comparison with the primary Pd(II) precursors (PhCN)2PdCl2 and Pd(OAc)2

The versatility of a Bedford-type palladacycle , namely [{Pd(micro-Cl){kappa2-P,C-P(OC6H(2)-2,4-tBu2)(OC6H(3)-2,4-tBu2)2}}2], as a primary Pd source, in combination with the ligand bis-1,1'-(diphenylphosphino)ferrocene (dppf) has been established in carbonylation reactions of aryl and heteroaryl bromides with methanol, piperidine and related nucleophiles. Palladacycle has been compared with other primary Pd sources, e.g. (PhCN)2PdCl2 and Pd(OAc)2. The efficacy of the carbonylation processes appear to be linked to the [Pd] concentration, substrate : catalyst ratio, CO pressure and reaction temperature. In amidocarbonylation, double carbonylation is observed for certain organohalides. In the case of 2,5-dibromopyridine, regioselective amination (Hartwig-Buchwald type) also occurs as a side-reaction.     

Solvent-free Heck and copper-free Sonogashira cross-coupling reactions catalyzed by a polystyrene-anchored Pd(II) phenyldithiocarbazate complex

A new polystyrene-anchored Pd(II) phenyldithiocarbazate complex is synthesized and characterized. This Pd-complex behaves as an efficient heterogeneous catalyst in the Heck coupling and copper-free Sonogashira coupling reactions under aerobic conditions. Furthermore, the catalyst shows good thermal stability and recyclability.     

Phase transfer Pd(O) catalyzed polymerization reactions. I. Synthesis of 1,2-(4,4′;-dialkoxyaryl) acetylene monomers and 1,4-Bis[2-(4′,4″-dialkoxyphenyl)ethynyl]benzene derivatives by phase transfer Pd(O)/Cu(I) catalyzed coupling reactions

Several 1,2-(4,4'-dialkoxyaryl)acetylene monomers containing similar or dissimilar substituents were prepared by one of three variations of a one pot phase transfer Pd(O)/Cu(I) catalyzed coupling of aryl halides with a protected acetylene. The three steps within a single flask involved first coupling of the appropriate 1-halo-4-alkoxybenzene derivative with 2-methyl-3-butyn-2-ol, followed by cleavage of the carbinol group to form an aryl acetylide, and finally a second coupling of an aryl halide with the aryl acetylide. Best results were obtained when elevated temperatures and solid-liquid phase transfer reaction conditions were used. Some 1,4-bis[2-(4',4”-dialkoxyphenyl)ethynyl]benzene compounds were also prepared.     

Suzuki-Miyaura reactions of arenediazonium salts catalyzed by PD(0)/C. One-pot chemoselective double cross-coupling reactions

The Suzuki-Miyaura cross-coupling of arenediazonium tetrafluoroborate salts with boronic acid partners catalyzed by Pd(0)/C is described as a practical and efficient alternative to classical homogeneous conditions. Reactions conducted in alcoholic solvents proved to be extremely fast using mild conditions. Additionally, we developed a chemoselective double Suzuki-Miyaura cross-coupling in a single reaction vessel allowing the synthesis of unsymmetrical terphenyls.     

Practical and efficient Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by recyclable Pd(0)/C

The first Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by 10% Pd(0)/C is described as an interesting alternative to classical homogeneous conditions. Most of the substrate reacted under mild condition at 25 degrees C under air in aqueous DME. The conditions described tolerate a wide range of iodoenones and boronic acids. Notably, the procedure features inexpensive reagents and solvents with low toxicity rendering the method environmentally benign. Additionally 10% Pd(0)/C could be recovered and efficiently reused at least five times without significant alteration of the yields of the cross-coupled product.     

Efficient Stille cross-coupling reaction catalyzed by the Pd(OAc)2/Dabco catalytic system

[reaction: see text] An efficient Pd(OAc)2/Dabco-catalyzed Stille cross-coupling reaction procedure has been developed. In the presence of Pd(OAc)2 and Dabco (triethylenediamine), various aryl halides including aryl iodides, aryl bromides, and activated aryl chlorides were coupled efficiently with organotin compounds to afford the corresponding biaryls, alkene, and alkynes in good to excellent yields. Furthermore, high TONs [turnover numbers, up to 980,000 TONs for the coupling reaction of 1-bromo-4-nitrobenzene and furan-2-yltributyltin] for the Stille cross-coupling reaction were observed.     

Efficient homo-coupling reactions of heterocyclic aromatic bromides catalyzed by Pd(OAc)2 using indium

Homo-coupling reactions of heterocyclic aromatic bromides smoothly proceeded with cat-Pd(OAc)₂, indium, and LiCl in DMF to afford exclusively symmetric biaryls possessing heterocyclic aromatic ring in good to excellent yields.     

Ethanol‐promoted reductive homocoupling reactions of aryl halides catalyzed by palladium on carbon (Pd/C)

Homocoupling reactions of aryl bromides or iodides proceeded smoothly with palladium on carbon (Pd/C) catalyst, ethanol and base in dimethyl sulfoxide (DMSO) to afford exclusively symmetric biaryls in good to excellent yields. Ethanol was first used as a reducing agent in situ to reduce the Pd²⁺/C species into Pd⁰/C active species to complete the catalytic redox cycle. It was found that ethanol can promote the Pd/C‐catalyzed reductive homocoupling of aryl iodides and bromides efficiently in the presence of base. A reaction mechanism has been put forward and discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Heck cross-coupling of vinyl heteroaromatic compounds with aryl and heteroaryl halides using Pd(II) complex under phosphine-free conditions

The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides and heteroaryl bromides is described using air and moisture stable N,N′,N″,O-tetrafunctional Pd catalyst under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were obtained in high to good yields.     

Synthesis of allyl-transition metal complexes by phase transfer catalyzed reactions of metal carbonyl halides: III. Considerations of the mechanisms

Mechanisms are proposed for the hydroxide ion-initiated reactions of metal carbonyl halides which lead to allyl-transition metal complexes under phase transfer conditions. Evidence is presented for intermediate anionic metallocarboxylic acids in reactions leading to η³-allyl products of molybdenum, iron, ruthenium and manganese, whereas η¹ complexes are shown to result from halide displacement reactions in which simple metal carbonyl anions are generated. In some cases phosphorus-containing ligands inhibit the hydroxide-promoted reactions of metal carbonyl halides with allyl bromide; a rationale involving decreased acidity of the carbonyl ligands is presented. Syntheses of η³-C₃H₅Mn(CO)₃P(OCH₃)₃ and η³-C₃H₅Mn(CO)₂[P(OCH₃)₃]₂ by phase transfer catalysis are also described.     

Transformations of tetracyclo [3.2.0.02,7.04,6]-heptane (quadricyclane) catalyzed by Pd2+ and Pd0 complexes

Conclusions In the presence of palladium(0) complexes, quadricyclone is converted to norbornadiene dimers and trimers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 475–477, February, 1985.     

Cationic polymerization with boron halides. V. Synthesis of poly(isobutylene-b-styrene) and poly(styrene-b-isobutylene)

Block copolymers of isobutylene and styrene, PIB-b-PSt and PSt-b-PIB, have been prepared by a two-step synthesis involving (1) preparation of terminally chlorinated (telechelic) polyisobutylene or polystyrene “prepolymers” by using the H₂O/BCl₃ initiator system and (2) blocking from these telechelic prepolymers a second polymer segment by using an alkyaluminum, e.g., Et₂AlCl coinitiator. The telechelic polyisobutylene and polystyrene contain tertiary and benzylic chlorine termini, respectively. Block copolymer characterization included detailed selective solvent extraction procedures, coupled with GPC determinations, PMR, solubility, and intrinsic viscosity studies. The synthesis of PIB-b-PSt and PSt-b-PIB provides direct chemical evidence for the presence and position of active chlorine termini in BCl₃-coinitiated olefin polymerizations.     

Fluorescent quenching of the 2-naphthoxide anion by aliphatic and aromatic halides. Mechanism and consequences of electron transfer reactions

The fluorescent excited state of the 2-naphthoxide ion (1) is quenched by aliphatic and aromatic halides according to an electron-transfer mechanism, with generation of the corresponding alkyl and aryl radicals by a concerted or consecutive C-X bond fragmentation reaction. Whereas bromo- and iodobenzene follow a concerted ET mechanism (C-X, BDE control), 1-bromonaphthalene exhibits a stepwise process (pi LUMO control). The photoinduced reaction of anion 1 with 1-iodoadamantane (2) in DMSO affords substitution products on C3, C6, and C8, 1-adamantanol, 1-adamantyl 2-naphthyl ether, and adamantane (3.2, 13.2, 12.2, 2.8, 2.5, and 14.1% yields, respectively). A complex mixture is also observed in the photochemical reaction of neopentyl iodide (3) with anion 1, which renders substitution on C1, C3, C6, C8, and 2-naphthyl neopentyl ether (8.1, 1.3, 19.1, 31.1, and 2.8% yields, respectively). The absence of reaction in the dark and the inhibition of the photoinduced reaction by the presence of the radical traps di-tert-butylnitroxide (DTBN) and 1,4-cyclohexadiene are evidence of a radical chain mechanism for these substitutions. On the other hand, only coupling at C1 is achieved by the photostimulated reaction of anion 1 with iodobenzene (5), to afford 41.9% of 1-phenyl-2-naphthol and 5.4% of disubstitution product. The regiochemistry of these reactions can be ascribed to steric hindrance and activation parameters.     

3+2] cross-coupling reactions of aziridines with isocyanates catalyzed by nickel(II) iodide

[reaction: see text]. Cycloaddition of aziridines with isocyanates proceeded smoothly in the presence of a nickel catalyst, and five iminooxazolidine derivatives were isolated in good yields. The best result was obtained when the reaction was carried out in the presence of NiI2, and a longer reaction time allowed the isomerization of the iminooxazolidine to the corresponding imidazolidinone derivatives.