Direct Alkenylation Research Articles

Microwave‐Assisted C‐2 Direct Alk­enylation of Imidazo[4,5‐b]pyr­idines: Access to Fluorescent Purine Isosteres with Remarkably Large Stokes Shifts

AbstractWe describe herein the first C‐2 direct alkenylation of the valuable 3H‐imidazo[4,5‐b]pyridine promoted by microwave‐assisted Pd/Cu co‐catalysis. The reaction is rapid and compatible with a wide range of functional groups either on the imidazo[4,5‐b]pyridine ring or on the styryl bromides thereby leading to the isolation of 23 compounds with moderate to good yields. The relevance of this method is demonstrated by its application to the synthesis of new cross‐conjuguated push–pull 2‐vinyl‐ and 2‐alkynylimidazo[4,5‐b]pyridines characterized by satisfactory fluorescence quantum yields and remarkable solvatofluorochromic properties.

Direct alkenylation of 2-substituted azaarenes with carbonyls via C[sbnd]H bond activation using iron-based metal-organic framework Fe3O(BPDC)3 as an efficient heterogeneous catalyst

A porous crystalline metal-organic framework Fe3O(BPDC)3 was synthesized from the reaction of biphenyl-4,4′-dicarboxylic acid and iron(III) chloride hexahydrate by a solvothermal method in the presence of acetic acid, and was characterized by using a variety of different techniques. The Fe3O(BPDC)3 could be used as an efficient heterogeneous catalyst in the synthesis of 2-alkenylazaarenes using the direct alkenylation of 2-substituted azaarenes with carbonyls via CH bond activation. The presence of acetic acid as a co-catalyst accelerated the transformation significantly. The Fe3O(BPDC)3 exhibited better performance in this transformation then other MOFs such as Fe3O(BDC)3, Cu2(OBA)2(BPY), Cu2(BDC)2(DABCO), Ni2(BDC)2(DABCO), Zn-MOF-74, and Cu2(NDC)2(DABCO). The Fe3O(BPDC)3 also exhibited higher catalytic activity than that of several homogeneous catalysts such as FeCl2, FeCl3, CuCl2, Zn(OAc)2, Zn(NO3)2, and Ni(OAc)2. The Fe3O(BPDC)3 catalyst could be recovered and reused several times in the synthesis of 2-alkenylazaarenes without a significant degradation in catalytic activity. To the best of our knowledge, 2-alkenylazaarenes was not previously synthesized via the direct alkenylation of 2-substituted azaarenes with carbonyls using heterogeneous catalysts.

Pd(0)-Catalyzed Direct C-H Functionalization of 2-H-4-Benzylidene Imidazolones: Friendly and Large-Scale Access to GFP and Kaede Protein Fluorophores.

The first one-pot synthesis of N-substituted 2-H-4-benzylidene imidazolones and their subsequent palladium-catalyzed and copper-assisted direct C2-H arylation and alkenylation with aryl- and alkenylhalides are described. This innovative synthesis is step-economical, azide-free, high yielding, highly flexible in the introduction of a variety of electronically different groups, and can be operated on large-scale. Moreover, the method allows direct access to C2-arylated or alkenylated imidazolone-based green fluorescent protein (GFP) and Kaede protein fluorophores, including ortho-hydroxylated models.

Direct alkenylation of alkylazaarenes with aldehydes through C(sp3)–H functionalization under catalytic InCl3 activation

Under the influence of InCl3 as a Lewis acid catalyst, a methodology on the C(sp3)–H functionalization of alkylazaarenes has been demonstrated through the activation of benzylic C–H bonds towards their addition reaction with the appropriate electrophiles. This methodology was chiefly applied in the direct alkenylation of primary and secondary benzylic C–H bonds of alkylazaarenes with aldehydes. A variety of alkenyl products were afforded in generally good yields including the starting alkenyl intermediate used in the synthesis of montelukast and other related molecules.

Site-Selective Intermolecular Oxidative C-3 Alkenylation of 7-Azaindoles at Room Temperature.

A previously unexplored palladium-catalyzed C-3 selective alkenylation of 7-azaindoles, performed in the presence of Pd(OAc)2 as the catalyst, PPh3 as the ligand, Cu(OTf)2 as an oxidative cocatalyst, and molecular oxygen (O2) as the terminal oxidant at room temperature, has been reported. This direct alkenylation strategy offers a new approach in functionalizing pharmaceutically important 7-azaindoles.

ChemInform Abstract: Palladium(II)‐Catalyzed Direct C—H Alkenylation of Thienothiophene and Related Fused Heteroarenes.

The palladium-catalyzed direct alkenylation of thieno[3,2-b]thiophene takes place regioselectively at C2. Symmetrically and unsymmetrically 2,5-dialkenylated thienothiophene derivatives can be prepared by the catalytic procedure. Related fused thienyl and carbazole derivatives also undergo regioselective direct alkenylation.

ChemInform Abstract: Solvent‐Free Ruthenium(II)‐Catalyzed C—H Activation: Synthesis of Alkenylarylpyrazole Derivatives.

AbstractThis direct alkenylation reaction is performed either under solvent‐free reaction conditions or by using a user‐friendly solvent.

Synthesis of pyrrole-based poly(arylenevinylene)s via Rh-catalyzed dehydrogenative direct alkenylation

Polycondensation via Rh-catalyzed dehydrogenative direct alkenylation was conducted. The introduction of a directing group, such as a 2-pyrimidinyl substituent, to the pyrrole monomer promoted a polycondensation reaction, giving rise to corresponding poly(arylenevinylene)s with a trans-configuration in good yields. The absorption and electronic properties of the polymers were examined.

Palladium-catalyzed direct alkenylation of 4-hydroxy-2-pyridones

The first direct 3-alkenylation of N-substituted 4-hydroxy-2-pyridones with unactivated alkenes is reported through a palladium acetate catalyzed, oxidative coupling.

Modified natural halloysite nanotube solely employed as an efficient and low-cost solid acid catalyst for alpha-arylstyrenes production via direct alkenylation

Owing to unique mesoporous/macroporous hollow nanotubular structure, relatively high specific surface area, abundant surface hydroxyl groups, ecological and biocompatibility as well as low cost and large availability, the natural halloysite nanotube (HNT) has attracted great attention in drug delivery, catalysis, adsorption, energy storage, etc. HNT was generally used as support in catalysis, but rare report for HNT being solely used as catalyst. In this work, we firstly reported that HNTS were solely employed as a solid acid catalyst for alkenylation of diverse aromatics with phenylacetylene to their α-arylstyrenes. It was found that the HNT with a facile ion exchange and calcination pretreatment demonstrated outstanding catalytic performance in alkenylation of p-xylene with phenylacetylene, and 95.6% of phenylacetylene conversion with 95.8% of selectivity toward α-(2,5-dimenthylphenyl) styrene was achieved. The HNT were characterized by N2 physisorption, transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3-TPD), pyridine infrared spectroscopy (Py-IR), and Inductively coupled plasma (ICP), and thermogravimetric analysis (TGA) techniques. Correlated the nature of HNTs to reaction results, it was revealed that the catalytic performance of HNT was significantly dependent on their acidic properties and textural feature notably affected by ion exchange times (NIE) and calcination temperature (TC). Especially, besides acidic properties, the nature of the formed mesopores on the walls of HNTs strongly affects the catalytic activity, selectivity and coke-deposition behavior. The appropriate acidic sites and their accessibility are essential for obtaining satisfactory catalytic performance. The modified HNT catalyzed alkenylation can be extended to diverse substrates with good catalytic properties for diverse α-arylstyrenes production. The combination of excellent catalytic properties and the facile regeneration of deactivated HNT by calcination process allows it to be a promising candidate for, but limited to alkenylation of aromatics with phenylacetylene to their α-arylstyrenes.

Palladium(II)-Catalyzed Direct C-H Alkenylation of Thienothiophene and Related Fused Heteroarenes.

The palladium-catalyzed direct alkenylation of thieno[3,2-b]thiophene takes place regioselectively at C2. Symmetrically and unsymmetrically 2,5-dialkenylated thienothiophene derivatives can be prepared by the catalytic procedure. Related fused thienyl and carbazole derivatives also undergo regioselective direct alkenylation.

Solvent‐Free Ruthenium(II)‐Catalyzed C–H Activation: Synthesis of Alkenylarylpyrazole Derivatives

AbstractThe RuII carboxylate complex Ru(MesCO2)2(p‐cymene) (Mes = mesityl) was found to be an efficient catalyst for the direct dehydrogenative alkenylation of N‐arylpyrazoles by using styrenes and acrylates in the presence of Cu(OAc)2·H2O in open air. The highly step‐economical C–H bond functionalization process is characterized by a wide substrate scope and significant chemoselectivity, which allowed direct alkenylation to be performed either under solvent‐free reaction conditions or by using a user‐friendly solvent system in which water was present as the major component. With less‐reactive styrenes, monoalkenylation took place, whereas with alkyl acrylates ortho‐dialkenylation occurred. This approach may provide new insight into the design of an environmentally benign method for the oxidative heterocoupling of N‐phenylpyrazole.

Ca(II) -catalyzed alkenylation of alcohols with vinylboronic acids.

Direct alkenylation of a variety of alcohols with vinylboronic acids has been accomplished using the air-stable calcium(II) complex Ca(NTf2 )2 under mild conditions with short reaction times. For reluctant transformations, an ammonium salt was used as an additive to circumvent the reactivity issue.

ChemInform Abstract: Room‐Temperature Direct Alkenylation of 3‐Arylsydnones.

A new efficient method for the direct alkenylation of 3-arylsydnones by palladium-catalyzed C–H functionalization was developed. The reaction proceeded smoothly at room temperature and delivered the product in yields up to 83 %.

ChemInform Abstract: Cobalt‐Catalyzed Direct Alkenylation of 2‐Methylquinolines with Aldehydes via C(sp3)—H Functionalization in Water.

AbstractNo products are formed starting from 2‐picoline or 2,6‐lutidine.

Sulphated mesoporous La2O3–ZrO2 composite oxide as an efficient and reusable solid acid catalyst for alkenylation of aromatics with phenylacetylene

Sulphated mesoporous La2O3–ZrO2 composite oxides (SO42−/meso-La2O3–ZrO2) were firstly prepared by a surfactant-assisted co-precipitation/hydrothermal crystallization with subsequent impregnation method (SACPHC-IM). The prepared SO42−/meso-La2O3–ZrO2 catalyst was employed as solid acid to catalyze direct alkenylation of p-xylene with phenylacetylene for clean production of α-arylstyrene. Various characterization techniques such as N2 adsorption–desorption, X-ray diffraction (XRD), FT-IR, NH3 temperature-programmed desorption (NH3-TPD), and pyridine-IR were employed to reveal the relationship between catalyst nature and catalytic performance. The as-prepared SO42−/meso-La2O3–ZrO2 catalyst shows much superior catalytic activity and similar selectivity to SO42−/meso-ZrO2, ascribed to increasing acid properties, enlarging specific surface area and increasing pore volume, reducing average crystalline size resulting from the promoting effect of adding La into ZrO2 matrix. Furthermore, the SO42−/meso-La2O3–ZrO2 catalysts were optimized by varying the atomic ratio of La/(La+Zr) from 0.05 to 0.2. The SO42−/meso-La2O3–ZrO2 catalyst with the 0.1 of optimum La/(La+Zr) atomic ratio exhibited excellent catalytic performance, ascribed to the increase in amount acid sites and pore size. The results for stability test demonstrated that close to 100% of maximum conversion can be achieved, and more than 80% of conversion can be maintained with the time on stream up to 780min. Through simple calcination treatment, the spent catalyst can be almost complete recovered. The developed SO42−/meso-La2O3–ZrO2 catalyst could be a potential candidate for α-arylstyrene production via acid catalyzed direct alkenylation of aromatics with phenylacetylene.

Rhodium(III)-catalyzed oxidative alkenylation of 1,3-dithiane-protected arenecarbaldehydes via regioselective C-H bond cleavage.

A Rh(III)-catalyzed direct alkenylation of 2-aryl-1,3-dithiane derivatives with alkenes has been developed. The 1,3-dithiane group can serve as an effective directing group for the exclusively monoselective alkenylation under mild oxidative conditions. The directing group is readily removable after the coupling event.

Ruthenium-Catalyzed Direct Oxidative Alkenylation of Arenes through Twofold C–H Bond Functionalization in Water: Synthesis of Ethyl (E)-3-(2-Acetamido-4-methylphenyl)acrylate

Ruthenium-Catalyzed Direct Oxidative Alkenylation of Arenes through Twofold C–H Bond Functionalization in Water: Synthesis of Ethyl (E)-3-(2-Acetamido-4-methylphenyl)acrylate

Palladium-catalyzed direct alkenylation of 2-methyl-4H-pyrido[1,2-a]pyrimidin-4-ones using oxygen as the oxidant

A direct C-3 alkenylation of 2-methyl-4H-pyrido[1,2-a]pyrimidin-4-ones through palladium-catalyzed C–H activation using oxygen as the terminal oxidant has been developed.

Palladium(II)-catalyzed direct alkenylation of dihydropyranones.

A palladium(II)-catalyzed direct alkenylation reaction of dihydropyranones was developed. Various substituted dihydropyranones could afford the desired products in reasonable yields. And different acrylates were found to be good coupling partners in this coupling reaction. A Pd(0)/Pd(II) catalytic pathway was proposed to be involved in this coupling reaction.