Showing papers in "Catalysts and Catalysed Reactions in 2006"

Ionic liquid as catalyst and reaction medium – a simple, efficient and green procedure for Knoevenagel condensation of aliphatic and aromatic carbonyl compounds using a task-specific basic ionic liquid

Abstract: The basic ionic liquid 1-butyl-3-methylimidazolium hydroxide, [bmIm]OH, efficiently catalyzes Knoevenagel condensation without requirement of any organic solvent. A wide range of aliphatic and aromatic aldehydes and ketones easily undergo condensations with diethyl malonate, malononitrile, ethyl cyanoacetate, malonic acid and ethyl acetoacetate. The reactions proceed at room temperature and are very fast (10-30 min). However, the most significant feature of this methodology is the condensation of aliphatic aldehyde with diethyl malonate, which is not very easy to achieve by conventional reagents, and was not addressed adequately in literature providing a general and convenient procedure.

Phosphine-free palladium catalyzed Mizoroki–Heck reaction using hydrazone as a ligand

Abstract: Glyoxal bishydrazones 1 and pyridyl-hydrazone 2b were prepared and examined as a ligand for the Mizoroki−Heck cross-coupling reaction of aryl halides and olefin. We found that PdCl2(MeCN)2/hydrazone ligand 1e was a phosphine-free efficient catalyst system for a variety of substrates to produce the Mizoroki−Heck coupling products in good yields.

Synthesis of 3-acyl-4-alkenylpyrrolidines by platinum-catalyzed hydrative cyclization of allenynes

Abstract: A series of nitrogen-tethered allenynes (‘5-aza-1,2-dien-7-ynes’) 1 were transformed to the corresponding 3-acyl-4-alkenylpyrrolidines 3 when treated with a catalytic amount of PtCl2 in MeOH at 70°. Initial Pt-promoted cyclization forms a nonclassical carbocationic intermediate. In contrast to the cycloisomerization in toluene, which produced the bicyclic cyclobutenes 2, the intermediate is intercepted by addition of an oxygen nucleophile to achieve the formal hydrative cyclization.

Efficient Michael addition of indoles using bismuthyl perchlorate as catalyst

Abstract: An efficient method for Michael addition of indoles has been developed using bismuthyl perchlorate (BiOClO 4 ·xH 2 O) as catalyst. The reaction proceeds to give 3-substituted indoles excellently stirring indoles and Michael acceptors in acetonitrile in the presence of the catalyst at room temperature or in much shorter reaction times under sonication at ambient temperature.

Asymmetric direct aldol reaction catalysed by l-prolinethioamides

Abstract: L-Prolinethioamides have been found to be active catalysts for direct aldol reactions of acetone with aromatic aldehydes, affording aldol products in good yields and with good enantioselectivities. They were prepared from L-proline and simple aliphatic and aromatic amines in optically pure form and in good overall yields. Studies employing ten catalysts allowed us to unequivocally establish the basic principles governing the outcome of the L-prolinethioamide-catalysed aldol reaction. In particular, the catalyst prepared from L-proline and (S)-phenylethylamine catalysed the reaction of acetone with 4-cyanobenzaldehyde in 57 % yield and 93 % ee (100 % ee at –78 °C). Most importantly, we found that steric interaction between the catalyst and a donor or an acceptor is crucial for the stereoselectivity of the aldol addition, while the unwanted formation of imidazolidinethione (from the catalyst and acetone or an aldehyde) was shown to decrease both the ee and the yield. The influence of the amine moiety (–CSNHR), different solvents and temperatures were studied, and we also found that there is a linear correlation between the optical purity of the catalyst and the ee of the aldol product, which supports the hypothesis that the reaction proceeds by the enamine–imine mechanism, involving only one molecule of the catalyst in the transition state. For the first time, the formation of 1,5-dihydroxypentan-3-one products (double addition products) was studied in detail. By precise optimisation we were able to show that the courses of the reactions of acetone with highly reactive aromatic aldehydes could be manipulated to give either the aldol products or 1,5-dihydroxypentan-3-one derivatives as the major product in moderate ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)