Current Organic Chemistry - Volume 22, Issue 19, 2018

Synthesis of aryl nitriles through nanoparticles catalyzed cyanation of aryl halides with K4[Fe(CN)6] as a non-toxic, non-hygroscopic, non-explosive, and inexpensive cyanating agent has drawn great attention in the past several years. This review discussed the recent advances in this interesting and fast-growing research arena. The review is divided into three major sections. The first section will cover Pd-NPs catalyzed reactions. The second focuses exclusively on Cu-NPs catalyzed cyanations. The third will discuss bimetallic-NPs catalyzed reactions. Literature has been surveyed until the end of 2017.

Background and Objectives: An environmentally benign method for the activation of an alcohol is based on its temporary conversion to a more reactive carbonyl compound by transition metal-catalyzed dehydrogenation. The use of homogeneous complexes in which noble metals were recently replaced by cheap, less toxic, earth-abundant metals (Mn, Fe, Co) enabled sustainable dehydrogenative coupling reactions of alcohols and X-nucleophiles (X: C, N, O). Greener synthesis of valuable chemicals (imines, amides, esters) occurred under acceptorless conditions, while direct alkylation of amines, alcohols and carbonyl compounds was achieved through borrowing hydrogen processes. Successful applications in the preparation of pharmaceutically interesting molecules (i.e. Piribedil) are discussed. The synthetic utility was further explored in the heterocycle synthesis. Aromatic (quinolines, pyrimidines, pyrroles) and non-aromatic heterocycles (lactones, lactams, cyclic amines and imides) were built up through single or multiple C-X bond formation.

Racemic and enantioselective synthesis of tetrahydroprotoberberine (THPB) alkaloids, a family of natural products showing a wide range of biological activity, have been based either on extension or enhancement of conventional methods or on new, recently developed tactics. Classical approaches to synthesize the THPB scaffold have utilized Bischler-Napieralski cyclization/reduction or Pictet-Spengler reactions to generate a benzyltetrahydroisoquinoline motif, followed by Mannich type condensation to obtain the tetracyclic THPB core. In recent developments, contiguously tetra-substituted ring D moieties and chiral auxiliaries to install the chiral center have been utilized to synthesize THPBs. The present review summarizes various approaches adopted to synthesize THPBs and their congeners, based on the sequence of formation of rings B and C.

Carboxylic acids are one type of the most common, readily available and structural diverse synthetic sources which gradually serve as versatile connection points in organic transformations. The decarboxylative reaction of carboxylic acids has attracted great attention in providing an efficient and powerful strategy for the construction of various valuable molecular skeletons. Over the past decades, a number of obvious and satisfactory achievements in the field have constantly emerged. The review mainly introduces recent advances on the decarboxylative reactions based on aliphatic, alkenylic or carbonic, aromatic and alkynylic acids as decarboxylative partners for the functionalization of C(sp3)-H, C(sp2)-H and C-heteroatom bonds since 2011.

Statins are popular drugs widely prescribed in Europe and the USA to control hypercholesterolemia and to prevent cardiovascular diseases. Among these drugs, synthetic statins possess the ability to absorb UV radiations in both UVA and UVB ranges. Light can induce drugs degradation leading to essential changes in their pharmaceutical properties and even to the loss of therapeutic activity, and/or to the formation of deleterious photoproducts. Drugs which exhibit photochemical reactivity may elicit undesired adverse effects. Knowledge of mechanisms involved in the molecular basis of these effects origin is of great importance for understanding chemical nature of occurring processes and their biological and medicinal implications, as well as for evaluating the photobiological risk associated with therapy in which drugs sensitive to light are involved. In this work, photophysical properties and photochemical behaviour of synthetic statins were reviewed, and findings regarding photodegradation mechanisms were summarised and critically discussed resulting in the revision of some previously reported facts as well as in proposing new schemes for the transformations of this important group of organic compounds. Moreover, possible biological consequences of statins photoinstability were also discussed. Besides the effect of light, statins' sensitivity to pH and resulting implications were discussed. Statins undergo pH-dependent interconversion between their pharmacologically active hydroxy acid and inactive lactone forms and it was shown that for both forms, drugs' interactions should be considered. Knowledge of the statins interconversion mechanisms is important for understanding how differences in the structures of their molecules can affect the activity of the drug at the molecular level and can have an impact on designing more effective novel and safe drugs.

A novel, simple and efficient laboratory scale continuous flow protocol has been elaborated for one-pot benzimidazole synthesis via a reductive cyclization method using the commercially available H-Cube Pro. Coupling with a stainless steel microreactor (4mL reactor volume), the acylation of o-nitroaniline was successfully joined in the hydrogenation step without any isolation or purification steps. This concept enabled a fully integrated process using a standard 5% Pt/C, sulfide catalyst for the reductive cyclization of 2-nitroacetanilide with quantitative yield. Compared with the previously reported batch processes, the present procedure facilitated efficient synthesis of a broad range of benzimidazole derivatives bearing functionalities sensitive to reductive cleavage and acidic conditions (10 compounds, 82 to >99% selectivity).

Due to error in printing, revised Fig. (4) should be included in the manuscript entitled “Removal of Tetracyclines from Water by Adsorption/ Bioadsorption and Advanced” published in Current Organic Chemistry, 2018, Volume 28, No. 10, page no. 1011.