Current Organic Chemistry - Volume 18, Issue 24, 2014

The synthesis of optically pure compounds remains a challenge in modern organic chemistry due to the great importance of single stereoisomers in the pharmaceutical, food, flavor, and fragrance industries. The crucial factor influencing the chemical yield and stereoselectivity of asymmetric reactions is the use of the appropriate chiral catalyst. Recently there has been a growing interest in the synthesis and modification of various chiral amine-functionalized compounds - especially aminoalcohols - to check their catalytic activity in various asymmetric reactions. On the basis of very few literature reports, it can be seen that aziridine-containing ligands exhibit a very high efficiency in reactions with organozinc reagents. In the existing review articles, this group of compounds has been described only randomly. The aim of the present paper is to review systematically the advances in the applications of chiral aziridine-containing derivatives as highly efficient catalysts in asymmetric synthesis, including also the results from our research group. In this review article, diverse aziridine-containing ligands such as aziridine alcohols, bis-aziridines, aziridine carbazides, and aziridine pyridines are described. The main attention is focused on the catalytic activity of the aforementioned ligands in the asymmetric reactions such as the addition of diethyl- and phenylethynylzinc to carbonyl compounds (aldehydes, enones), asymmetric allylic alkylation, direct asymmetric aldol condensation, nitroaldol (Henry) reaction, cyclopropanation and others.

The electrophilic C-H bond substitution of arenes (ArH) by the linear nitronium (ONO+) ion or nitrating agents (Y-NO2), giving nitroarenes (ArNO2), has been of interest in organic chemistry for many years. The reactions were found to take place via a nitroarenium ion [Ar(H)NO2]+ (σ-complex). Research in the recent twenty years has revealed that two reactive intermediates, a charge-transfer complex (π-complex) [ArH, NO2]+ or [ArH, YNO2]+ and an ion-radical pair [ArH+. , NO2•], are produced consecutively in the aromatic nitration prior to formation of the σ-complex [Ar(H)NO2]+. The full mechanism for this classical type of reactions has been established. Electrophilic aromatic substitution reactions of various structurally related electrophiles, such as dithionitronium NS2+ and zwitterionic Cl2SO+--AlCl3 adduct, have been discovered and studied most recently. The related nucleophilic aromatic substitution has been further studied recently. Effective biological applications of several types of functionalized aromatic compounds have been developed in the recent decade.

The synthesis of complex natural products from simple and common intermediates has been one of the major goals in synthetic organic chemistry. Toward this objective, if such simple scaffolds are suitably decorated with diverse functional groups they present opportunities not only to synthesize the target compounds but also construct the close analogues to investigate the biological properties. The Morita-Baylis-Hillman (MBH) reaction is an organocatalyzed C-C bond forming reaction that leads to multifunctional products thereby offering viable alternatives for employing them for other complexity generating reactions. This property has been extensively utilized for the synthesis of natural products of microbial, animal, terrestrial, and marine origins. Simultaneously, MBH adducts are precursors to several drug molecules or their intermediates. This comprehensive review assimilates applications of the Morita-Baylis-Hillman reaction for the synthesis of different natural products and drug molecules.

In this critical overview of what kind of organic chemistry is currently performed by biotechnology, the examples of the production of high added value molecules for pharmaceutical industry, of biomaterials and their modification as well as of commodities are discussed. The major strengths as well as weaknesses of this kind of approach in comparison to current organic chemistry achievements are discussed. The prospects of future development and collaborative approach between pure organic synthesis and biotechnological transformations are also developed.

A microbial and enzymatic process for xylitol production that initiates from D-glucose occurs by virtue of a three-step process in which D-arabitol is the first intermediate product and D-xylulose is the second. To date, the steps of the formation of D-arabitol and the conversion of xylitol from D-xylulose are key points of departure for promoting the overall process for xylitol production from D-glucose. This review provides comprehensive insights regarding potential methods of xylitol production from D-glucose, which might be an alternative to the classical process that utilizes D-xylose as substrate.

The design and synthesis of graphene-based nanocomposites have drawn enormous attention in recent years owing to their unique structural properties. Here, we describe a simple hydrothermal procedure to fabricate Cu-graphene nanocomposites as a catalyst for direct hydroxylating benzene to phenol in the presence of hydrogen peroxide. The nanocomposites present high catalytic activity and short reaction time, attributing to the uniform diameters of the Cu nanoparticles and their homogeneous distribution on surfaces of graphene sheets. The effects of graphene content, molar ratio of H2O2 to benzene, and reaction temperature on the catalytic performance of the prepared Cu-graphene were studied. Notably, the Cugraphene nanocomposites can contribute a conversion rate of 13.8 % and a phenol selectivity of 92.9 %. In particular, the reaction time was greatly shortened to 0.2 h, which is pretty faster than other reported Cu-based catalysts, indicating the promising application of Cugraphene nanocomposites in the hydroxylation of benzene.

This report explores Suzuki-Miyaura coupling under microwave irradiation, using a new generation of catalyst that is based on natural phosphate (NP) impregnated by palladium. This catalyst was prepared by the treatment of natural phosphate with bis(benzonitrile)palladium(II) chloride in acetone at room temperature. The catalyst displayed high catalytic activity for the Suzuki-Miyaura coupling of aryl bromides and chlorides with aryl boronic acids in pure water and with the use of microwave irradiation. The low-cost and availability of the solid support, mild reaction conditions, high yields of desired products, recyclability of the catalyst and short reaction times are the notable features of these methods.