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Five-Membered Fused Polyheterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Palladium-catalyzed carbon-heteroatom formation can be coupled with direct, oxidative coupling of two carbon-hydrogen bonds as well. Ohno et al. [106] reported this reaction for the synthesis of carbazoles from aniline and aryl-triflates (Scheme 53). This consecutive carbon-nitrogen and carbon–carbon bond formation reaction occur with a single palladium catalyst produced from palladium acetate where C-N coupling is carried out under an inert atmosphere, followed by the incorporation of acetic acid and oxygen to mediate the subsequent carbon-hydrogen activation/cyclization. This reaction can tolerate various substituents, with product selectivity favoring activation of the less sterically hindered carbon-hydrogen bond. Ryu et al. [133] reported a related approach for the preparation of benzothiophenes.
Direct (Hetero)Arylation Polymerization for the Preparation of Conjugated Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
J. Terence Blaskovits, Mario Leclerc
In keeping with history, the first report of a polymer synthesized by Pd-catalyzed direct C–H activation both occurred with a series of poly(3-alkylthiophene)s and took place over a decade after the first studies of the C–H activation of heterocycles by Itahara in the 1980s. This first report of a direct arylation polymerization, by Lemaire and colleagues, consisted of the homopolymerization of 2-iodo-3-alkylthiophene using conditions developed for the Heck reaction.83 The monomer was chosen for the reason that it possessed both a carbon-halogen (C–X) bond and an aryl C–H bond, the two functional groups necessary for a direct arylation coupling, with the expectation that it would react upon itself and form a homopolymer. The reaction conditions consisted of palladium acetate (Pd(OAc)2) as the catalyst, potassium carbonate (K2CO3) as the base, and tetrabutylammonium bromide (TBAB) as an additive, using DMF as the solvent. This yielded a polymer with a low number-average molecular weight (Mn) of 3 kDa and a regioregularity (RR) of 90% (Figure 5.4a). RR, which indicates the degree of selective couplings and structural uniformity of the polymer, is explained in greater detail later in this chapter. The reaction conditions used were chosen because, at the time, the authors believed that the reaction proceeded by a Heck-like carbo-palladation mechanism.
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
The 2-(trans-3-pentenyl)-phenol was cyclized in the presence of palladium(II) catalyst and copper acetate/oxygen oxidant to afford 3,4-dihydro-2-vinyl-2H-1-benzopyran readily.[106] The 2-allylphenols by intramolecular oxypalladation afforded benzofurans and their 2,3-dihydro-derivatives in the presence of oxygen in catalytic amounts of palladium chloride or palladium acetate.[107] Products were formed in optically active form through the formation of in situ pinanylpalladium complexes when worked with (1R,5R)-2(10),3-pinadiene or α-pinene. The S-(+)-2,3-dihydro-2-vinylbenzofurans were formed predominantly from 2-(trans-2-butenyl)phenols (Scheme 32), while the (R)-(+)-2,3-dihydro-2-vinylbenzofurans (Scheme 33) were obtained as prevailing enantiomer from cis isomer, although the heterocyclization occurred with a low degree of enantioselectivity (up to 29% ee). The palladium(0) was not formed from palladium(II) with oxygen–copper acetate system or tert-butylhydroperoxide.[108–112] The 2-allylphenols were utilized for the synthesis of substituted 2-methylbenzofurans in the presence of copper acetate/lithium chloride as oxidant system and palladium acetate as catalyst in dimethylformamide as solvent.[113,114]
BNPs@Cur-Pd as a versatile and recyclable green nanocatalyst for Suzuki, Heck and Stille coupling reactions
Published in Journal of Experimental Nanoscience, 2020
Muhammed Ali Jani, Kiumars Bahrami
BNPs (15 g) were added to the 20 mL of solvents (1:4 v/v H2O/EtOH) and were ultrasonicated for 15 min. Then, 15 mL of (3-chloropropyl)triethoxysilane (CPTES) was added to the mixture and under the nitrogen atmosphere refluxed at 50 °C for 8.5 h. Next, a 10 mL of curcumin solution was added to the mixture and refluxed at 70 °C for 14 h to obtain nanoparticles. The orange-colored solution was centrifuged and washed with ethanol, then dried at 70 °C. To anchor Pd on the BNPs@Cur support, BNPs@Cur powder (8 g) was dispersed and sonicated 15 min in the mixture of H2O/EtOH (20 mL, 1:1 v/v H2O/EtOH). Then, palladium acetate (0.085 g) was added to the reactor and stirred for 24 h at ambient temperature. The dark gray BNPs@Cur-Pd powder was obtained after separation, by washing with ethanol and drying it in an oven.
Synthesis and properties of antiferroelectric and/or ferroelectric compounds with the –CH2O group close to chirality centre
Published in Liquid Crystals, 2019
Magdalena Urbańska, Paweł Perkowski, Mateusz Szala
A mixture of (S)-1-[(octyl-2-oxy)methyl]-4-(1,3,2-dioxaborinane-2-yl)benzene (16 g; 53 mmol), 4-iodophenol (11 g; 50 mmol) and potassium carbonate (20.7 g; 150 mmol) in 210 ml of acetone and 70 ml of water were refluxed and boiled for 15 min. The solution was then cooled to 35°C and palladium acetate was added as a catalyst. The colour changed to brown. The solution was then heated until boiling for 3 h. The reaction was carried out in a protective atmosphere of nitrogen. After cooling, 10% hydrochloric acid was added to remove excess potassium carbonate. After the evolution of CO2 stopped, the mixture was poured into water and extracted with methylene chloride. It was then dried over magnesium sulfate and methylene chloride was evaporated until dry. The product was crystallised from a mixture of ethanol-hexane and anhydrous ethanol. The crystallisation did not succeed, so crude (S)-4ʹ-hydroxy-4-[(octyl-2-oxy)methyl]biphenyl was used for further reactions.