Direct arylations potassium acetate

The intermolecular direct arylation of simple benzenes was also evaluated [12]. Under conditions established for the fluorinated substrates, none of the desired cross-coupled product was formed. With the goal of increasing the amount of soluble base in the reaction mixture, varying amounts of different carboxylic acids were added. Both the amount and the type of acid was found to influence significantly the reaction outcome, with larger acids used in substoichiometric amounts providing superior outcomes. For example, as the steric bulk is increased from acetic acid to pivalic acid, an increase in conversion is noted. Under optimal conditions, addition of 30 mol% pivalic acid results in 100% conversion of the aryl bromide and an 82% isolated yield of benzene direct arylation is obtained. To rationalize the reactivity, it was proposed that the potassium pivalate may behave as... 

Recently, Zhang and coworkers reported a direct palladium-catalyzed C-2 arylation of indoles with potassium aryltrifluoroborate salts [204]. Remarkably, the direct arylation took place at room temperature when acetic acid was used as the solvent. 

Arylation of Quinoline N-Oxides and Pyridines N-Oxides. An efficient protocol to directly arylate quinoline A-oxides was developed using palladium acetate as the catalyst and potassium carbonate as the hase. A survey of different phosphines demonstrated that the sterically less encumbered di-tert-butyl(methyl)phosphonium tetrafluoroborate provides higher yields relative to tri-iert-hutylphosphine. Using this protocol, 15 quinohne A-oxides were arylated in good to excellent yields (eq 1). ... 

The title compound is commonly used as a base in transition metal-catalyzed reactions. Because these reactions involve multiple elementary steps, KOAc may act as a base in many different ways, and the precise mechanism of deprotonation may not always be known. A study on the influence of base on the palladium-black-catalyzed methoxycarbonylation of aryl iodides identified potassium acetate as a suitable base. This method has been widely adopted, and both sodium and potassium acetate are commonly used (e.g., eq 29). Alternatively, the acetate base may directly remove a proton from a metal center. For example, the Heck reaction (e.g., eq 30) generates a palladium(II) complex that bears hydride and halide ligands, and generation of the catalytically active palladium(0) corr5>lex requires deprotonation with stoichiometric base (eq 31). 

Palladium-catalyzed Direct Arylation of Pyridine N-Oxides, Pyrazine N-Oxides, Pyridazine N-Oxides, Pyrimidine N-Oxides, and Thiazole N-Oxides. Pyridine W-oxides can be efficiently ary-lated at the C2 position using aryl halides as the electrophile, palladium acetate as the catalyst, tri-tert-butylphosphonium tetraflu-oroborate as the ligand, and potassium carbonate as the base (eq 19). In this protocol, 3 equiv of pyridine Al-oxide are utilized to generate the corresponding 2-aryl derivatives. ... 

Two methodologies for the direct C-2 arylation of thiazoles have been reported. The first one is mediated by both palladium and copper <07T1970>. Thus, the C-2 arylation of thiazole and benzothiazole with aryl iodides is carried out using copper iodide (2 equiv.) and a catalytic amount of palladium acetate under base-free conditions. The other method involves copper-catalyzed arylation with aryl iodides in the presence of lithium t-butoxide <07JA12404>. In general, reactions with lithium tert-butoxide provide better yields than those with potassium fert-butoxide. In addition, arylation with phenyl bromide, chloride or tosylate fails to provide any desired arylation products. 

A new method for the conversion of aldopyranosides to 5-thioaldopyranosides is exemplified in Scheme 3 the isomeric acyclic intermediates, e.g. compound 33, could be separated, inverted at C-5 and cyclized stereoselectively, thus offering access to several different products. 5-Thio-D-arabinose (34) has been synthesized from D-arabinose in six standard reaction steps. Synthesis of 5-thio-L-fucopyranose, as the tetraacetate 35, from D-arabinose required chain-extension at the non reducing end which was achieved by diastereoselective reaction of aldehyde 36 with methyl lithium the D-aftro-product 37 was then treated sequentially with tosyl chloride and potassium thioacetate. A number of aryl a-5-thiofucosides, as well as p-nitrophenyl a-l,5-dithiofucoside, were prepared from 1-acetate 35 directly or via a trichloroacetimidate. These compounds were used to demonstrate the importance of sulfur in the ring and oxygen at the... 

The analgesic properties of various phenylacetic acids continue to stimultae the development of new routes to compounds of this type. Aryl bromides can be converted directly into phenylacetates by palladium-catalysed coupling with ethyl a-(tri-n-butylstannyl)acetate in the presence of zinc bromide. Aryl iodides can also be directly coupled to the potassium... 

The or//io-palladation of 3,4-dioxygenated benzylic tertiary amines by lithium tetrachloropalladate can be directed exclusively to either C-2 or C-6. Substitution at C-6 prevails when AcO, methylenedioxy, PhCH20, methoxymethyl ether, or HO substituents are attached to C-3, whereas palladation occurs exclusively at C-2 when C-3 bears methylthiomethyl ether or phenylthiomethyl ether substituents. The resulting organopalladium compounds are crystalline solids, stable to air and moisture, and can readily be carbonylated, alkylated, arylated, Kinetic studies of the acetoxylation of arenes by potassium peroxydisulphate and acetic acid in the presence of (2,2 -bipyridyl)palladium(ii) acetate catalyst have led to a revision of the mechanism. The reaction is now thought to proceed via... 

---