Current Organic Chemistry - Volume 16, Issue 24, 2012

The review describes preparation of P,N-bidentate ligands without a P–N bond and their use in asymmetric catalysis. Diverse types of aminophosphines are considered with emphasis on P,N-ferrocene ligands, phosphino-oxazolines and phosphinopyridines. The following major synthetic approaches to aminophosphines and related compounds are summarized: (i) via lithiation, (ii) the use of Grignard reagents, (iii) nucleophilic substitution using metal phosphides, (iv) Staudinger method, (v) hydrophosphination of α,β-unsaturated carbonyl compounds, (vi) Cu- and Pd-catalyzed C-P bond formation reactions, and (vii) reactions of cyclopalladated complexes with metal phosphides and HPPh2. Highlights of aminophosphine applications in asymmetric synthesis include their use in hydrogenation, hydrosilylation, and hydroboration reactions as well as in various transformations leading to a C-C bond formation such as Suzuki coupling, Meerwein-Eschenmoser-Claisen rearrangement, Mukaiyama aldol reaction, Tsuji allylation and ethylene oligomerization.

This review provides an overview of methods that lead to the substitution of halogens from rings of halogenated heterocycles by hydrogen. The first part of the review treats the subject matter from the viewpoint of the method used for the hydrodehalogenation reaction, while the second part is devoted to site selective reductive processes.

Biotransformation is a broad and constantly growing field of biotechnology, which encompasses enzymatic, microbial and biomimetic catalysis. Use of biocatalysis for some chemical synthesis steps has unique advantages over traditional chemistry, most notably the possibility of achieving higher product selectivity under mild process conditions. This review discusses critical aspects of biotransformation of toxic organic compounds and suggests some guidelines for experimental planning which could significantly impact product yield. The relative effectiveness of bioconversion depends on the characteristics of microbes and their enzymes, nutritional conditions, environmental parameters (T, pH, pO2), exposure to chemicals which can inhibit or induce enzyme levels, effects of extreme environments (e.g., non-aqueous media), and the kind of product isolation techniques used. Some of these and other factors affecting the efficiency of biotransformation as well as the most promising approaches to transformations of troublesome compounds are described. Recent advances in the use of both synthetic and natural porphyrins as biomimetic catalysts for biotechnological purposes and chemical syntheses are also discussed.

We screened for selective inhibitors of mammalian DNA polymerase (Pol) species from natural products. We then identified compounds that are potential anticancer agents based on Pol inhibition. In this review, the focus is on symbiotic microorganisms that grow on wild marine plants and which could be used as a new screening source for anticancer compounds. The fungal strains were isolated from wild marine plants such as seaweeds and sea mosses collected in Japan. Nine novel compounds were isolated from the cultured broth extracts of isolated fungal strains. These compounds showed bioactivities such as selective inhibition of mammalian Pol activity among 10 mammalian Pol species and suppression of proliferation of human cancer cells while having no effect on the growth of normal human cells. The probability of discovering novel compounds from such sources is high. Therefore, microorganisms derived from wild marine plants appear to be a good screening source for bioactive compounds compared with other naturally occurring materials.

Solid-emissive materials have found many applications in various fields, especially in the development of organic lightemitting diodes (OLED) and solid-state sensory devices. Currently, the biggest limitation is the availability of highly solid-emissive materials, which meet the requisites of good chemical- and photo-stability. Among all the chromophores developed until now, BODIPY derivatives (4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene) have been recognized as the best candidates for practical applications, due to their excellent photophysical properties and high stability. To maintain the fluorescence of Boron difluorides in solid state, numerous strategies are adopted, focusing on inhibition of intermolecular planar π-π interactions. This review mainly deals with solid-emissive BF2 complexes, concerning molecular design, synthesis, photophysical properties, and their applications.

Chiral (R)-(-) and (S)-(+)-8-amino-5,6,7,8-tetrahydroquinoline, hereafter defined (R)-CAMPY and (S)-CAMPY, have proved to be valuable chiral ligands in Ru(II) precatalysts for the reduction of prochiral ketones by asymmetric hydrogen transfer AHT. These ligands bear chiral information on an alkyl ring fused to a pyridine and therefore have a flat nature, characterized by a high conformational rigidity. It represent the first application in AHT of a member of a family of ancillary ligands already known as starting material for medicinal compouds. The reaction with [RuCl2PPh3] furnished the (OC-6-14)-[RuCl2(PPh3)2(CAMPY)] which evolved to (OC-6-42-C)- [RuCl2(PPh3)2(CAMPY)] in refluxing toluene. The absence of a suitable crystal for X-ray structure was easily overcame by a combination of routines 2D-NMR experiments based on an unprecedent 4-bond P-H coupling. The formation of (OC-6-42-C)- [RuCl2(PPh3)2(CAMPY)] is totally stereoselective at the chiral metal center; the same behavior is followed when triphenyl phosphines are displaced by chelating diphosphines like Ph2P(CH2)4PPh2 (DPPB) and Ph2P(CH2)3PPh2 (DPPP). The flat and rigid nature of CAMPY alone gave catalyst able to reduce acetophenone with moderate e.e.; substitution of triphenylphosphines in the complex with an achiral chelating diphosphines produce Ru-catalysts witch gave enantioselectivities up to 96%.

The formation of oxygenated (quinone) and oxidative (polymer) products in the reaction of selected phenols with hydrogen peroxide catalysed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides ((TAP)FeIIICl) in 3:1 mixture of dichloromethane and hydroxyl ionic liquids (1-(2-hydroxyethyl)-3-methyl imidazolium and 2-hydroxyethyl ammonium ionic liquids) depend on the electron donating and withdrawing group on porphyrin rings, type of ionic liquids and phenols. Oxygenated products were obtained from iron(IV) oxo radical cationic intermediate by heterolytic cleavage of the O-O bond of (TAP)Fe(III)-OOH in the reaction of iron(III) porphyrin with H2O2 in [HOEMIm]PF6 and [HOEMIm]BF4 based hydroxyl ILs. Polymeric products were obtained from homolytic cleavage of the O-O bond of (TAP)FeIII-OOH in the reaction of iron(III) porphyrin with H2O2 in [HOEMIm]OH and [HOEMIm]OAc based hydroxyl ILs. The catalytic efficiency of iron(III) porphyrin increases in 3:1 binary mixture of dichloromethane and imidazolium based hydroxyl IL in comparison with 3:1 binary mixture of dichloromethane and ammonium based hydroxyl ionic liquids. The coordination of [HOEMIm]+ cation in [HOEMIm]PF6 and [HOEMIm]BF4 ILs and OH- and OAc- anions in [HOEMIm]OH and [HOEMIm]OAc ILs with (TAP)FeIIICl have been studied by UV-vis and 1H NMR spectroscopy.

The application of photocatalytic reactions in organic synthesis has attracted extensive attentions because of recent developments in environmentally benign synthetic processes. For the first time, an organic pigment (C. I. Pigment Green 8) was used as selective photocatalyst to accomplish the photocatalytic hydroxylation of phenol to catechol (CAT) and hydroquinone (HQ) with the assistance of UV irradiation at room temperature. The prepared photocatalysts were characterized by FT-IR spectrum and UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and the result found that the photocatalyst exhibits excellent adsorption ability both in the ultraviolet and visible light region. The effects of various affecting-parameters, such as catalyst amount, H2O2 amount, co-solvents and reaction time, on the photocatalytic hydroxylation of phenol were studied to optimize the reaction conditions. The desired products (CAT and HQ) on the photocatalyst can be facilitated with an increase in the selectivity. In this study, the conversion efficiency of phenol could reach high up to 87.8% with a total selectivity of 73.0% as well as the yield of 37.0% and 27.4% for CAT and HQ, respectively. The reaction is a photo-Fenton like process, and the iron ions cycle between Fe2+ and Fe3+ occurs with the light irradiation.