Current Organic Chemistry - Volume 16, Issue 8, 2012

The advent of host-guest catalysis brought about the prospect of a complementary mode of catalysis, with the potential for savings in cost, time and energy, easier experimental procedures, and reductions in chemical waste. Water-soluble calix[n]arene catalytic systems provide additional options in biphasic catalysis for organic chemistry and process engineering. The use of calix[n]arene as hostguest catalysis developed in recent years has shown promising results since calix[n]arenes have been widely used as three-dimensional molecular platforms for the design of artificial molecular receptors, due to the availability of cheap starting materials and the facile modification of the calix[n]arene structure at the wide and narrow rims.

Three commercially available lipases from Candida rugosa (OF and MY from Meito Sangyo Co., and CRL from Sigma- Aldrich Co.) were used for the enantioselective esterification reaction of (R,S)-ibuprofen with 1-propanol and 2-propanol in saturated cyclohexane as reaction medium. All tested lipases preferentially catalysed the esterification of the S-enantiomer of ibuprofen. However, each one of the analysed lipases demonstrated differences in the catalytic activity. Lipase OF showed the highest conversion degree, and the best enantioselectivity was observed for MY and CRL lipases. The influence of temperature, reaction time and addition of N,N’- dicyclohexylcarbodiimide (DCC) on the enantioselectivity and on the conversion degree in the enzymatic esterification was studied and the optimal condition for enantioselective esterification was evaluated. Moreover, the application of new commercial cellulose-based tris(3,5-dimethylphenylcarbamate) HPLC chiral column was demonstrated for effective separation, qualification and quantification of both substrates and products within one chromatographic analysis.

(+)-Zwittermicin A is a highly polar, water-soluble aminopolyol antibiotic isolated from the soil-born bacterium B. cereus with significant activity against phytopathogenic fungi. The rising interest in zwittermicin A as a “green” biopesticide, has stimulated studies of its unique biosynthesis, mechanism of action and its organic synthesis. This review summarizes the current state of this antibiotic. A main focus of this review is the description of the chemistry of this compound including its synthesis.

The heterogeneous catalytic hydrogenation of nitriles is an important industrial process for the production of diverse amines. The reaction scheme based on the von Braun and Greenfield proposals has been widely accepted for many years and it remains the most frequently cited reaction sequence for the formation of secondary and tertiary amines via the hydrogenation of nitriles. Over the past decade, there has been a stream of published papers that, using modern scientific techniques, have intensively investigated the detailed mechanism underlying the surface reactions of heterogeneously catalyzed nitrile hydrogenation and the surface intermediates. On the one hand, the results of these studies bring some light to this issue; on the other hand, entirely new, unanswered questions arise from new knowledge. The studies suggest that the mechanism of nitrile hydrogenation on solid catalysts is much more complicated than expected based on the reaction formalism of von Braun and Greenfield. Unfortunately, there are as yet no physicochemical studies available that could confirm in a straightforward manner the intimate details of the reaction mechanism of surface reactions. In this review, the various speculative mechanisms proposed for heterogeneous nitrile hydrogenation are discussed. It seems very likely from current knowledge that aminocarbene complexes and aldimines, coordinated to a metal via the π-system of a C=N double bond and/or via the nitrogen lone pair, will prevail among the surface intermediates suggested for nitrile hydrogenation on palladium or platinum, whereas hydrogenation on a cobalt or nickel surface will likely be associated with the formation of nitrene intermediates. This duality provides a satisfactory explanation for the selectivity differences between metal catalysts in nitrile hydrogenation to primary amines.

The present work contains a comprehensive overview of methods published in the period 2005-2011 for the preparation of polyheterocycles containing isoindole-fused ring(s). New synthetic routes are described for the construction of heterocycle-condensed isoindole derivatives with regard to the ring positions and types of these annelated ring systems. On the occasion of the 60th birthday of Prof. Dr. Ferenc Fulop academician.

Several 1-aryl-hydroxy and dihydroxyisochromans were synthesized by a two-steps procedure based on the oxa-Pictet- Spengler reaction performed for the first time in dimethyl carbonate (DMC) from phenethyl alcohols and substituted benzaldehydes followed by the regioselective aromatic hydroxylation/oxidative aromatic demethylation with 2-iodoxybenzoic acid (IBX)/sodium dithionite (Na2S2O4) system. Some of them showed a novel pattern of hydroxylation degree into A ring. All synthesized isochromans were tested about their radical scavenging activity by 2,2-diphenyl-2-picrylhydrazyl radical (DPPH.) method. Experimental results showed that dihydroxyisochromans were more active than the corresponding phenolic or guaiacolic parent compounds confirming the key role of the catecholic moiety for the antioxidant activity.