The dimeric Pd(I)-complex [Pd(μ-Br)(P(t)Bu3)]2 was found to be highly active for catalyzing double-bond migration in various substrates such as unsaturated ethers, alcohols, amides, and arenes, under mild conditions. It efficiently mediates the conversion of allylic esters into enol esters, rather than inserting into the allylic C-O bond. The broad applicability of this reaction was demonstrated with the synthesis of 22 functionalized enol esters.

In the presence of catalytic amounts of magnetite nanopowder, mixtures of aromatic and aliphatic carboxylic acids are converted selectively into the corresponding aryl alkyl ketones. As byproducts, only carbon dioxide and water are released. This catalytic cross-ketonisation allows the regioselective acylation of aromatic systems and, thus, represents a sustainable alternative to FriedelCrafts acylations.Keywords: aryl alkyl ketones; catalysis; cross-ketonisation; decarboxylation; iron Aryl alkyl ketones are among the most important synthons in the industrial manufacture of commodities, [1] fine chemicals, and pharmaceuticals.[2] Simple derivatives, at early stages of the chemical value creation chain, are synthesised almost exclusively via FriedelCrafts acylation of arenes, because the low cost of this reaction is unrivalled to date.[3] However, two main issues are associated with this approach. Its low regioselectivity leads to the co-manufacture of large amounts of isomeric by-products, and the use of acyl chlorides as starting materials activated with superstoichiometric amounts of salt mediators (e.g., AlCl 3 ) is responsible for the formation of enormous quantities of salt waste.Regioselective and less waste-intensive acylations, e.g., cross-couplings [4] of sensitive arylmetal reagents with either preformed [5] or in situ-generated [6] carboxylic acid derivatives are widely used to access highervalue synthetic intermediates. However, their high cost precludes their application in the manufacture of base chemicals. This is also the case for alternative approaches, such as Heck-type reactions, [7] or the Pdcatalysed decarboxylative cross-coupling of a-oxocarboxylate salts with aryl halides.[8] Thus, a clear need remained for a broadly applicable, regioselective and waste-minimised aryl alkyl ketone synthesis starting from simple, inexpensive, and widely available chemicals.As a solution to this long-standing problem, we envisioned a catalytic process in which an aromatic and an aliphatic carboxylic acid are cross-coupled under release of CO 2 and water, to selectively give the aryl alkyl ketone (Scheme 1). In such a decarboxylative cross-ketonisation, the carboxylate groups would predefine the position of bond formation, potentially allowing a selective synthesis of any desired regioisomer. If mediated by catalytic amounts of an inexpensive metal with high selectivity for hetero-over homocoupling, the overall process would be advantageous both from economical and ecological standpoints.The decarboxylative homoketonisation of aliphatic carboxylic acids is an established strategy for the preparation of symmetrical dialkyl ketones or cyclic alkanones.[9] State-of-the-art protocols involve gasphase transformations at temperatures above 350 8C at solid catalysts, for example, CaO, ZnO, MgO, [10] TiO 2 , [11] ZrO 2 , [12] MnO, [13] Fe 2 O 3 , [14] or rare earth metal oxides [15] on SiO 2 -, Al 2 O 3 -, or pumice-based supports. However, if equimolar mixtures of aromatic and aliphatic carboxylic acids ar...

No abstract

An efficient two-step palladium catalysed synthesis of 2,5-disubstituted oxazoles is reported.

Extremely small, monodisperse, and spheric maghemite (γ-Fe2O3, 2–3 nm) and manganese (4–7 nm), cobalt (3–5 nm), and zinc ferrite (5–7 nm) nanocrystals are directly accessible on a large scale starting from inexpensive metal powders and octanoic acid by thermolysis in a high-boiling solvent. Bigger particle size is obtainable by prolonged reaction time according to the Ostwald ripening principle. The superparamagnetic nanocrystals and their assembly have been characterized by transmission electron microscopy, powder X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, and energy-dispersive X-ray spectroscopy.

Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201303426. Figure 1. Examples of biologically active alkylidenephthalides. Scheme 1. Synthetic entries to alkylidenephthalides.

Neue Richtung: Die Carboxygruppe von Benzoesäuren steuert deren ortho‐Acylierung mit Carbonsäureanhydrid in Gegenwart eines Rhodiumkatalysators (siehe Schema; cod=Cyclo‐1,5‐octadien). Diese ortho‐Acylierung bildet eine Ergänzung zu der meta‐Selektivität von Friedel‐Crafts‐Reaktionen. Die Produkte können durch Protodecarboxylierung in Arylketone überführt werden.

Compared to Pd(II) or Pd(0) catalysts, the Pd(I) dimer permits the double bond migration of a wide range of unsaturated substrates which can be further hydrogenated in the presence of a chiral system to optically active saturated esters.