Regioselective Pd Research Articles

Pd-Catalyzed C(sp2)-H/C(sp2)-H Coupling of Limonene.

Limonene undergoes a regioselective Pd(II)-catalyzed C(sp2)-H/C(sp2)-H coupling with acrylic acid esters and amides, α,β-unsaturated ketones, styrenes, and allyl acetate, affording novel 1,3-dienes. DFT computations gave results in accord with the experimental results and allowed for the formulation of a plausible mechanism. The postfunctionalization of one of the coupled products was achieved via a large-scale Sonogashira reaction conducted under micellar catalysis.

A chemo- and regioselective Pd(0)-catalyzed three-component spiroannulation.

A chemo- and regioselective Pd(0)-catalyzed spiroannulation has been successfully developed. The key feature of this method is the use of readily available 1,2-dihaloarenes, alkynes and 2-naphthols for the rapid assembly of spirocarbocyclic molecules. Mechanistic studies revealed that this domino reaction proceeded through a cascade of oxidative addition to Pd(0), alkyne migratory insertion, and 2-naphthol-facilitated dearomatizing [4+1] spiroannulation.

Site-Selective Nanoreactor Deposition on Photocatalytic Al Nanocubes.

Photoactivation of catalytic materials through plasmon-coupled energy transfer has created new possibilities for expanding the scope of light-driven heterogeneous catalysis. Here we present a nanoengineered plasmonic photocatalyst consisting of catalytic Pd islands preferentially grown on vertices of Al nanocubes. The regioselective Pd deposition on Al nanocubes does not rely on complex surface ligands, in contrast to site-specific transition-metal deposition on gold nanoparticles. We show that the strong local field enhancement on the sharp nanocube vertices provides a mechanism for efficient coupling of the plasmonic Al antenna to adjacent Pd nanoparticles. A substantial increase in photocatalytic H2 dissociation on Pd-bound Al nanocubes relative to pristine Al nanocubes can be observed, incentivizing further engineering of heterometallic antenna-reactor photocatalysts. Controlled growth of catalytic materials on plasmonic hot spots can result in more efficient use of the localized surface plasmon energy for photocatalysis, while minimizing the amount and cost of precious transition-metal catalysts.

Dioxazolones as masked ester surrogates in the Pd(ii)-catalyzed direct C-H arylation of 6,5-fused heterocycles.

A simple and effective Pd(ii)-catalyzed regioselective C(2)-H arylation of 6,5-fused heterocycles with dioxazolones as a masked ester surrogate under mild conditions is reported. The significance of the arylation is highlighted by the new reactivity demonstrated in dioxazolones via proximal C-H activation of the cyclic carbonate of the hydroxamic acid functionality under protic conditions.

Asymmetric Total Synthesis of (+)-(3E)-Pinnatifidenyne via Abnormally Regioselective Pd(0)-Catalyzed Endocyclization.

The asymmetric total synthesis of the marine natural product (+)-(3E)-pinnatifidenyne was accomplished. The key features of the synthesis involve the construction of an eight-membered cyclic ether by the abnormally regioselective Pd(0)-catalyzed cyclization, the installation of a double bond in the oxocene skeleton by sequential in situ deconjugative isomerization, and the efficient introduction of the crucial chloride mediated by the substrate-controlled diastereoselective reduction.

Mild and Regioselective Pd(OAc)2-Catalyzed C-H Arylation of Tryptophans by [ArN2]X, Promoted by Tosic Acid.

A regioselective Pd-mediated C–H bond arylation methodology for tryptophans, utilizing stable aryldiazonium salts, affords C2-arylated tryptophan derivatives, in several cases quantitatively. The reactions proceed in air, without base, and at room temperature in EtOAc. The synthetic methodology has been evaluated and compared against other tryptophan derivative arylation methods using the CHEM21 green chemistry toolkit. The behavior of the Pd catalyst species has been probed in preliminary mechanistic studies, which indicate that the reaction is operating homogeneously, although Pd nanoparticles are formed during substrate turnover. The effects of these higher order Pd species on catalysis, under the reaction conditions examined, appear to be minimal: e.g., acting as a Pd reservoir in the latter stages of substrate turnover or as a moribund form (derived from catalyst deactivation). We have determined that TsOH shortens the induction period observed when [ArN2]BF4 salts are employed with Pd(OAc)2. Pd(OTs)2(MeCN)2 was found to be a superior precatalyst (confirmed by kinetic studies) in comparison to Pd(OAc)2.

ChemInform Abstract: Pyrrole as a Directing Group: Regioselective Pd(II)‐Catalyzed Alkylation and Benzylation at the Benzene Core of 2‐Phenylpyrroles.

AbstractThe Pd‐catalyzed ortho‐alkylation of 2‐phenylpyrroles (I) and (IX) gives rise to 2‐substituted benzenes (III) and (XI), whilst the benzylation of substrates (XII) affords 2,6‐dibenzylbenzenes (XIII).

Pyrrole as a Directing Group: Regioselective Pd(II)-Catalyzed Alkylation and Benzylation at the Benzene Core of 2-Phenylpyrroles.

Pyrrole has been employed for the first time as a directing group in the Pd(II)-catalyzed ortho-functionalization of C(sp(2))-H bonds. A variety of substituted 2-phenylpyrroles were successfully methylated, alkylated, or benzylated in the ortho-position of the benzene ring, yielding the respective 2-substituted pyrrol-2-yl benzenes (36 examples, 51-93% yield). Neither additives nor additional ligands were required to perform the reaction, which was routinely conducted with PdBr2 as the catalyst and Li2CO3 as the base. Mechanistically, there is evidence that precoordination of palladium to the pyrrole enables the regioselective ortho-attack.

Stepwise Polychlorination of 8-Chloro-BODIPY and Regioselective Functionalization of 2,3,5,6,8-Pentachloro-BODIPY.

An effective, stepwise methodology for polychlorination of BODIPY using trichloroisocyanuric acid (TCCA) in acetic acid was developed. In this way, selectively substituted di-, tri-, tetra-, and pentachloro-BODIPYs 2-5 were prepared. The pentachloro-BODIPY is shown to undergo regioselective Pd(0)-catalyzed Stille and Suzuki coupling reactions, first at the 8-position followed by the 3,5- and then the 2,6-positions; nucleophilic substitution reactions occur first at the 8- followed by the 3,5-positions, while the 2,6 are unreactive.

Synthesis of 3,8-dichloro-6-ethyl-1,2,5,7-tetramethyl-BODIPY from an asymmetric dipyrroketone and reactivity studies at the 3,5,8-positions.

The asymmetric BODIPY 1 a (BODIPY=4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), containing two chloro substituents at the 3,8-positions and a reactive 5-methyl group, was synthesized from the asymmetric dipyrroketone 3, which was readily obtained from available pyrrole 2 a. The reactivity of 3,8-dichloro-6-ethyl-1,2,5,7-tetramethyl-BODIPY 1 a was investigated by using four types of reactions. This versatile BODIPY undergoes regioselective Pd(0) -catalyzed Stille coupling reactions and/or regioselective nucleophilic addition/elimination reactions, first at the 8-chloro and then at the 3-chloro group, using a variety of organostannanes and N-, O-, and S-centered nucleophiles. On the other hand, the more reactive 5-methyl group undergoes regioselective Knoevenagel condensation with an aryl aldehyde to produce a monostyryl-BODIPY, and oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) gives the corresponding 5-formyl-BODIPY. Investigation of the reactivity of asymmetric BODIPY 1 a led to the preparation of a variety of functionalized BODIPYs with λmax of absorption and emission in the ranges 487-587 and 521-617 nm, respectively. The longest absorbing/emitting compound was the monostyryl-BODIPY 16, and the largest Stokes shift (49 nm) and fluorescence quantum yield (0.94) were measured for 5-thienyl-8-phenoxy-BODIPY 15. The structural properties (including 16 X-ray structures) of the new series of BODIPYs were investigated.

ChemInform Abstract: Highly Regioselective Three‐Component Palladium‐Catalyzed Synthesis of 5‐Vinyloxazolidin‐2‐ones from 2,3‐Allenyl Amines, Organic Iodides, and Carbon Dioxide.

A highly regioselective Pd(0)-catalyzed synthesis of 5-vinyloxazolidin-2-ones from 2,3-allenic amines, organic iodides, and CO2 under mild conditions has been developed. (C) 2013 Elsevier Ltd. All rights reserved.

Highly regioselective three-component palladium-catalyzed synthesis of 5-vinyloxazolidin-2-ones from 2,3-allenyl amines, organic iodides, and carbon dioxide

A highly regioselective Pd(0)-catalyzed synthesis of 5-vinyloxazolidin-2-ones from 2,3-allenic amines, organic iodides, and CO2 under mild conditions has been developed.

ChemInform Abstract: Ligated Regioselective PdII Catalysis to Access β‐Aryl‐Bearing Aldehydes, Ketones, and β‐Keto Esters.

AbstractThe title acid‐free method is based on the coupling of allyl alcohols with arylboronic acids to access dihydrochalcones, dihydrocinnamaldehydes, and β‐arylketones with more tolerance of functionalities than previously reported.

Ligated Regioselective PdII Catalysis to Access β‐Aryl‐Bearing Aldehydes, Ketones, and β‐Keto Esters

AbstractBy employing ligands in the PdII‐mediated arylative isomerization of allyl alcohols, a milder and regioselective access to the versatile building blocks β‐aryl aldehydes and ketones was developed. This new and chelation‐controlled protocol enabled the compatibility of wide range of functionalities to generate dihydrochalcones, α‐benzyl‐α′‐alkyl acetones, dihydrocinnamaldehydes, and α‐benzyl β‐keto esters (from Baylis–Hillman adducts). A practical multigram synthesis of an intermediate for Propafenone was also demonstrated.

A versatile synthetic approach to grandisol monoterpene pheromone

A versatile and efficient synthetic procedure for the grandisol pheromone library has been established. The key feature of our synthesis involves a versatile and highly regioselective Pd(0)-catalyzed intramolecular allylic alkylation for the key cyclobutane skeleton of grandisol. In this connection, the concise synthesis of (±)-grandisol as well as mechanism study of Pd(0)-catalyzed regioselective cyclization as a key reaction have also been accomplished.

ChemInform Abstract: Synthesis of 2-(o-Hydroxyaryl)-4-arylthiazoles by Regioselective Pd(0)-Catalyzed Cross-Coupling.

The difunctional substrate 2,4-dibromothiazole 2 was transformed into the title compounds 1 by consecutive Pd(0)-catalyzed cross-coupling reactions. Aryl zinc reagents which were prepared by ortho-lithiation of compounds 3 and subsequent transmetalation were used as carbon nucleophiles in the first coupling reaction. By this means, an aryl substituent was attached to the 2-position (50–62% yield). A succeeding cross-coupling with arylboronic acids 4 occurred at the 4-position of the intermediate 4-bromothiazoles 5 (76–97% yield).

ChemInform Abstract: Regioselective Pd(0)‐Catalyzed Hiyama Cross‐Coupling Reactions at Dihalo‐Substituted Heterocycles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Regioselective Pd(0)-Catalyzed Hiyama Cross-Coupling Reactions at Dihalo-Substituted Heterocycles

The regioselectivity of the Hiyama cross-coupling reaction at various dihalo-substituted heterocycles has been studied. Methyl 2,3-dibromo-5-furancarboxylate and n-octyltrifluorosilane were employed to find optimum reaction conditions [CsF; Pd2dba3/P(2-furyl)3 as catalyst, 80-150 ˚C in toluene or benzene] for the desired transformation. Subsequent experiments with the title compounds and with different primary alkyltrifluorosilanes illustrate the generality of this regiochemical process.

A Multifaceted Phosphate Tether: Application to the C1−C14 Subunit of Dolabelides A−D

A phosphate tether approach to the C1-14 subunit of dolabelide is described. The phosphate tether serves a multifaceted role mediating several processes, including (i) diastereotopic differentiation via RCM, (ii) selective CM by imparting Type III behavior to the exocyclic olefin, (iii) regioselective hydrogenation, and (iv) regioselective Pd(0)-catalyzed reductive opening of the bicyclic phosphate. Overall, this strategy uses orthogonal protecting- and leaving-group properties innate to phosphate esters to rapidly assembly the titled subunit.

Pd(0)-Catalyzed Coupling−Cyclization of 2-(2‘,3‘-Allenyl)acetylacetates and Organic Halides: An Efficient Synthesis of 4,5-Dihydrofuran Derivatives

[reaction: see text] Highly chemo- and regioselective Pd(0)-catalyzed coupling-cyclization of 2-(2',3'-allenyl)acetylacetates with organic halides using K3PO4 as base in DMF efficiently afforded 4,5-dihydrofuran derivatives in moderate to excellent yields, with a selectivity of >97:3.