The osmium-catalyzed dihydroxylation of various olefins using molecular oxygen or air as the
stoichiometric oxidant is reported. Aromatic olefins yield the corresponding diols in good to excellent
chemoselectivities under optimized pH conditions (pH = 10.4−12.0). Air can be used under moderate pressures
(3−9 bar) instead of dioxygen as the reoxidant. By increasing the oxygen content of the solution, it is possible
to achieve highly efficient conversion at low catalyst amount (catalyst/substrate = 1:4000). Tri- and
tetrasubstituted olefins are oxidized at pH > 11 to give the corresponding 1,2-diols in good to very good
yields without requiring the addition of sulfonamides or other hydrolysis agents. Studies of the dihydroxylation
of functionalized olefins demonstrate that the reaction conditions tolerate a variety of functional groups. In the
presence of dihydroquinine or dihydroquinidine derivatives (Sharpless ligands), asymmetric dihydroxylations
occur with lower enantioselectivities than tose of the classical K3[Fe(CN)6] reoxidation system.
Primary aromatic amides were prepared by a palladium-catalyzed aminocarbonylation reaction of aryl halides in high yields (70-90%) using formamide as the amine source. The reactions require a palladium catalyst in combination with a nucleophilic Lewis base such as imidazole or 4-(dimethylamino)pyridine (DMAP). Aryl, heteroaryl, and vinyl bromides and chlorides were converted to the primary amides under mild conditions (5 bar, 120 degrees C) using 1 mol % of a palladium-phosphine complex. Best results were obtained in dioxane using triphenylphosphine as the ligand and DMAP as the base. For activated aryl bromides, a phosphine-to-palladium ratio of 2:1 was sufficient, but less reactive aryl bromides or aryl chlorides required ligand-to-palladium ratios up to 8:1 in order to stabilize the catalyst and achieve full conversion. The influence of catalyst, base, solvent, pressure, and temperature was studied in detail. The mechanism of the reaction could be clarified by isolating and identifying the reaction intermediates. In addition, methylamides and dimethylamides were prepared by the same method using N-methylformamide and N,N-dimethylformamide as the amine source.
Dihydroxylations of simple alkenes were carried out for the first time in excellent yields and selectivities with molecular oxygen as oxidant [(Eq. (a)]. Both oxygen atoms are used productively and are incorporated into the product in this transition metal catalyzed alkene oxidation.
Organic pigments are important crystalline substances, and their properties and applications rely on size and shape control. Pigment Yellow 181 (PY181) is an industrial azo pigment that is light and weatherfast and suitable for high temperature processing. One disadvantage is its needle‐like shape in the default β‐phase, which makes the pigment difficult to process in industry, e.g., in polymer melts, where a spherical structure would be ideal. Here, we show for the first time, that polymer‐induced liquid precursor structures can be formed even in association to a chemical reaction. Furthermore, it is demonstrated that biomineralization principles can be exploited for the generation of advanced functional materials, such as pigments with novel complex morphology and different properties. Stable PY181 microspheres of nanoplates in the β‐phase were obtained in mixed solvents of water and isopropanol by direct azo coupling under the directing influence of a designed copolymer additive aminobenzoylaminobenzamide‐acetoacetyl‐poly(ethylene imine)‐block‐poly(ethylene glycol) (ABABA‐acetoacetyl‐PEI‐b‐PEG).
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