Current Organic Chemistry - Volume 16, Issue 10, 2012

The journal ‘;Current Organic Chemistry’ is in its sixteenth year of publication. Over the years it has grown to be a reputable journal and has achieved an Impact Factor of 2.920. In the past years, Current Organic Chemistry has published individual reviews as well as special Hot Topic issues. This Special Anniversary issue presents the updated highly cited articles on the latest developments in various topics published in ‘Current Organic Chemistry’ which are of considerable interest to the scientific community. We hope this collection of timely reviews will be of great interest to organic chemists. I would like to thank all the authors for their excellent contributions, and the referees for helping to improve their quality.

The catalytic C-C bond activation by rhodium complexes has found a wide application in organic synthesis. The course of the reaction is usually controlled by the proper ligand environment enabling processes that are otherwise not feasible under classical conditions of organic chemistry. The C-C bond activation can be achieved by the release of ringstrain in cycloalkanes (e.g. compounds possessing three- and four-membered rings), in case of non-strained C-C bonds it could be directed by a neighboring functionality (e.g. carbonyl group), or through initial C-H activation (e.g. aldehyde decarbonylation). Many of these processes have been implemented in syntheses of various natural compounds. The use of chiral ligands has recently enabled to carry many of these reactions in an enantioselective manner.

In the past decades, chiral sulfoxides have been finding increasing use, reflecting a wide interest in both convenient auxiliaries in asymmetric synthesis and products with biological properties containing a chiral sulfinyl group. Since the breakthrough of the groups of Kagan and of Modena (1984) who discovered that modified titanium(IV) isopropoxide - diethyltartrate catalyst systems (known as “modified Katsuki-Sharpless reagents”) are capable of asymmetric oxidizing of prochiral sulfides by alkylhydroperoxides, plethora of modifications and practical applications of titanium based catalyst systems for the asymmetric oxidation of sulfides to sulfoxides emerged. Diverse catalysts based on titanium complexes with other chiral ligands as well as on other transition metal complexes appeared, especially in the last fifteen years. The aim of this review is to cover the progress in transition metal catalyzed asymmetric sulfides oxidations achieved since the milestone discoveries of early 1980s and to bring out the main trends of this important field of modern catalytic chemistry.

Oxygenated steroids are bioactive compounds and valuable intermediates in the synthesis of biologically active products and APIs. This review will cover the literature from 2005/06 to the present concerning allylic oxidation, epoxidation and syn-dihydroxylation of alkenes, alcohol oxidation, and remote functionalization reactions of steroidal substrates.

The Prins reaction and the Prins cyclization have stood out as important synthetic strategies, and here the latest advances in this topic are reviewed. Different mineral acids, Lewis acids, organic acids and supported acidic materials have been employed as promoters for this type of transformation, the reaction with paraformaldehyde being the most considered one. Without any doubt, the Prins cyclization forming oxygenated heterocycles is one of the most common tranformations, and many studies have been reported on this topic. The acid-promoted Prins cyclization of an oxocarbenium ion generated in situ from suitable starting materials in order to produce the corresponding tetrahydropyrans have been extensively studied and employed in the total synthesis of a wide number of natural products. Additionally, the Prins cyclization have been employed in the synthesis of five, seven, eight and nine membered rings. The aza version of this reaction has been also considered, the analogous aza-cyclization allowing the synthesis of piperidine derivatives, which are widely distributed in natural products.

This updated version of a 2008 review presents work in the still developing field of dehydrogenative coupling reactions of phosphines. Catalytic phosphorus-element bond formation via dehydrocoupling has rapidly expanded since the first discoveries in the mid 1990s. A survey of the available catalysts, P-P and P-E products, and mechanistic understanding is presented with emphasis on the emerging synthetic applications of this reaction.

In the paper the introduction pointing out the important role of viologens is followed by two chapters concerning rotaxanes with a thread incorporating viologens, and those with a ring built from viologens. In the next two chapters dendrimers containing viologens as a core and those with viologens localized in their apical positions are presented. The fifth chapter deals with viologens noncovalently bound with cucurbiturils, calixarenes and cyclodextrins. The final chapter shows other viologen containing compounds; it mainly concerns assemblies of their nanostructured films.

Oximes are acetylcholinesterase reactivators of use in poisoning with organophosphorus inhibitors of cholinesterase (OPIChE: (organophosphates and organophosphonates). They are clinically used as an adjunct to atropine in such exposure. Clinical experience with oximes is, however, disappointing. This paper reviews available data concerning the ability of established and new oximes to reactivate cholinesterases inhibited by two differently substituted prototypical organophosphates: ethyl- and methyl-paraoxon. The intrinsic toxicity of oximes is quantified in vitro by measuring the concentration required to inhibit red blood cell (RBC) cholinesterase activity by 50% (IC50). Reactivation ability is assessed in vitro via the IC50 shift graph. The slope of the shift graph (tan α) is used to quantify the magnitude of the protective effect (nM IC50 increase per μM reactivator). The ranking of reactivating potencies of the examined oximes determined with methyl-paraoxon as an inhibitor is essentially the same as the ranking obtained using ethyl-paraoxon as an inhibitor. In the in vitro model used, the presence of ethyl versus methyl substituents does not seem to significantly alter the ability of the examined oximes to reactivate the esterase. In vitro derived results were subsequently validated in vivo in rats using ethyl-paraoxon and methyl-paraoxon as cholinesterase inhibitors and various oximes as reactivators. Mortality data were compared and hazard ratios calculated using Cox proportional hazards model. Overall, the ability of in vitro testing (tan α determinations) to predict in vivo protection by oximes is limited.