Abstract: A variety of electrostatically enhanced 3- and 4-pyridylborate salt catalysts are reported and show significant improvement over an activated noncharged neutral control compound. Their nucleophilicity in a stoichiometric SN2 reaction and catalytic performance in a urethane synthesis are evaluated along with three methods for rapidly evaluating the basicity of these species. That is, qualitative titrations in CH2Cl2 and CHCl3 were carried out, two separate solution-state IR studies in CCl4 and CDCl3 are reported, and the proton affinities of the anionic components of the salts were computed. Charge differences between the anion and its protonated zwitterionic conjugate acid are evaluated along with the highest occupied molecular orbitals of the anions in relationship to some of the surprising reactivity findings that were observed in the two kinetic studies.
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With bis-triphenylphosphine-palladium(II) chloride; sodium carbonate; triphenylphosphine; In 1,4-dioxane; water; at 90℃; for 12h;Inert atmosphere;
General procedure: The appropriate mono-, di- or tri-iodo TPA derivative (300 mg)and pyridin-4-ylboronic acid were dissolved in a mixture ofdioxane/H2O (25 mL, 4/1). Ar was bubbled through the mixture for10 min and [PdCl2(PPh3)2], Na2CO3 and PPh3 were added. The reaction mixture was stirred at 90 °C for 12 h. The cooled reactionmixture was diluted with H2O (50 mL) and extracted with CH2Cl2(2 50 mL). The combined organic extracts were thenwashed withbrine and dried (Na2SO4). Finally, the solvents were evaporatedunder vacuum and the crude product was purified by columnchromatography (SiO2, appropriate eluent).
With (1,1'-bis(diphenylphosphino)ferrocene)palladium(II) dichloride; sodium carbonate; In 1,4-dioxane; water; at 90℃; for 4h;
General procedure: To a solution of and halide in the indicated solvent is added boronic acid or ester, carbonate base, and palladium catalyst at room temperature. After stirring at 100 °C overnight, the mixture is cooled and concentrated.Following Procedure B using 5 (150 mg, 1.04 mmol), 4-pyridinylboronic acid (191 mg, 1.56 mmol), sodium carbonate (220 mg, 2.1 mmol), dioxane (5 mL), water (0.5 mL), and Pd(dppf)Cl2 (50 rng, 0.07 mmol ), react at 90 °C for 4 hours and then purify with silica gel column chromatography (EA:PE = 1 :2) to give A3S as a solid (100 mg, 78percent yield). (MS: [M+H]+ 188.1)
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