Palladium acetate-lithium bromide

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

In analogy with the oxybromination reaction of allenyl alcohols, allenyl acids 12 afforded five- and six-membered lactones 13 on treatment with lithium bromide in the presence of palladium acetate (Scheme 17.8) [7, 8],... 

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. 

Tri- and tetra-substituted dihydropyranones and furanones have also been synthesized by a Wacker/Mizoroki-Heck domino process (Scheme 8.72). Gouvemeur and cowoikers [151] very recently prepared these kinds of compounds using different palladium sources, copper acetate as redox mediator, oxygen as oxidant and lithium bromide as additive. The coupling of two electron-poor substrates, ethyl acrylate and -hydroxy alkynones 294, led to the desired compounds 295a-e in moderate yields. 

Condensation of 2-methylquinolone 9 with dialdehyde 10 (1.5 mol equiv), in the presence of acetic anhydride afforded, after elimination of approximately 20% of Ws-adduct, compound 11 in 65% overall yield as a pure -isomer. Grignard reaction with vinylmagnesium bromide 12, under standard conditions, gives the expected scc-alcohol 13, which is condensed with methyl-2-iodobenzoate 14, in the presence of palladium acetate and lithium acetate in DMF, to yield ketone 15. 

Indoles.—Formation. Phenacyltriphenylarsonium bromide, Ph3AsCH2COPh Br , reacts with aniline to give 2-phenylindole. o-Tolyl isocyanide (306) is selectively lithiated at the methyl group by lithium di-isopropylamide at —78°C warming the product to room temperature, followed by aqueous workup, yields indole almost quantitatively. The ester (307) cyclises to the indole (308) in the presence of palladium acetate and triphenylphosphine. Treatment... 

Craft and Gung developed a paUadium-catalyzed transannular [4+3] cycloaddition route in which all of the rings of cortistatins are prepared in one step from a single macrocyclic precursor (Scheme 19.50) [114]. Exposure of macrocyclic allene 233 to a catalytic amount of palladium (II) acetate in the presence of excess lithium bromide resulted in the formation of 238 as a single isomer in 37% yield. This is the first report of a transannular [4+3] cycloaddition. The proposed mechanism is shown in Scheme 19.50. The formation of allene-palladium complex 234 affords a a-allylpalladium intermediate, which rapidly isomerizes to the 7i-allylpalladium intermediate 235. This can then undergo intramolecular cycloaddilion via an endo (compact) transition strucmre 236 to give bromonium ion 237. The loss of a proton results in the formation of the observed product 238. Cycloadduct 238 was readily converted into the tetracyclic core skeleton of cortistatins 239 by selective reduction of the olefin formed by cycloaddition with furan, followed by reductive debromination. 

Seven procedures descnbe preparation of important synthesis intermediates A two-step procedure gives 2-(HYDROXYMETHYL)ALLYLTRIMETH-YLSILANE, a versatile bifunctional reagent As the acetate, it can be converted to a tnmethylenemethane-palladium complex (in situ) which undergoes [3 -(- 2] annulation reactions with electron-deficient alkenes A preparation of halide-free METHYLLITHIUM is included because the presence of lithium halide in the reagent sometimes complicates the analysis and use of methyllithium Commercial samples invariably contain a full molar equivalent of bromide or iodide AZLLENE IS a fundamental compound in organic chemistry, the preparation... 

Methylphenyl)benzothiazole (80IC762) and 2-benzylbenzothiazole (95ICA(239)125) can be cyclopalladated. In the latter case, cylopalladation occurs upon reaction with palladium(II) acetate and gives the product 80. With lithium chloride, sodium bromide, or sodium iodide, a series of three products of substitution of the acetate group 81 (X = C1, Br, I) results. Pyridine, 2- and 3-methylpyridine, 2,6- and 3,5-dimethylpyridine cause the transformation of the chelate complexes 81 (X = C1, Br, I) and formation of the mononuclear products 82 (R = z= R" = = R = H, X = Cl, Br, I ... 

Aldehyde Imidazole Potassium fluoride Oxalyl chloride Methyl magnesium bromide Acetic anhydride Sodium hydrogen carbonate Hydrogen hydrochloride Lithium hydroxide Tetrabromomethane Tetramethylammonium acetate Benzylchlorobis(triphenyl-phosphine)palladium (II)... 

A round-bottom flask was charged with a mixture of 2,6-dimethylphenyl trifluoromethanesulfonate (127.1 mg, 0.5 mmol), anhydrous lithium chloride (4 mmol), copper(I) bromide (0.2 mmol), and dichlorobis(triphenylphosphine)-palladium(II) (10-20 mol %) suspended in DMF (2.5 cm ). 2-Methoxyphenyl-tributyltin (1-1.5 mmol) was added to the mixture in two portions, i.e., at the beginning of the reaction and at half completion. A crystal of 2,6-bis(l,l-dime-thylethyl)-4-methylphenol (BHT) was added as an inhibitor of radical processes, and the mixture was then heated to reflux, under argon, during 8 - 24 h. Water and Et20 (25 cm ) was added, and the organic phase was washed subsequently with hydrochloric acid solution (1.5 mol dm , 6 x 20 cm ), a saturated solution of potassium fluoride (5 x 20 cm ), and finally dried over anhydrous sodium sulfate. Evaporation to dryness furnished a residue and that was suspended in ethyl acetate and the insoluble material was filtered off. The filtrate was... 

Addition of tributylstannyl-lithium to crotonaldehyde and protection of the resulting alcohol with chloromethyl methyl ether gives the stannane (192), which reacts with both alkyl and aryl aldehydes RCHO to form specifically the t/rr o-hydroxy-enol ethers (193). These latter compounds have been used to prepare tra/i5-4,5-disubstituted butyrolactones by hydrolysis and subsequent oxidation. Palladium-catalysed carbonylation of RX in the presence of organotin species constitutes a useful synthesis of unsymmetrical ketones, and in the example reported this year RX is an arenediazonium salt. The reaction, which is basically an aromatic acylation, proceeds in good to excellent yield. Another Pd-catalysed reaction of aromatics, this time aryl bromides, is their reaction with acetonyltributyltin (194), prepared from methoxytributyltin and isopropenyl acetate, to give the arylacetones (195). ... 

---