Recent Advances in Manganese(III)-Assisted Radical Cyclization for the Synthesis of Natural Products: A Comprehensive Review.

Natural products play an important part in synthetic chemistry since they have many pharmacological properties and are used as active drug compounds in pharmaceutical chemistry. However, synthesis of these complex molecules is difficult due to the requirement of various synthetic steps, which include highly regio- and stereoselectivity. Therefore, oxidative radical cyclization assisted by manganese(III) acetate serves as an important step in obtaining spiro-, tricyclic, tetracyclic, and polycyclic derivatives of these compounds. Manganese(III)-based reactions offer a single-step regio- and stereoselective cyclizations and α-acetoxidations, reducing the number of synthetic steps. Also, the manganese(III)-mediated oxidative free radical cyclization method has been successfully applied for the synthesis of cyclic structures found in many natural products. This article presents a broad overview of manganese(III)-based radical reactions of natural products as a key step in overall synthesis. The authors have classified natural product synthesis processes assisted by manganese(III) acetate as intermolecular, intramolecular, oxidation, acetoxidation, aromatization, and polymerization reactions, respectively.

The effect of pH on the interlayer distances of elongated titanate nanotubes and their use as a Li-ion battery anode.

Titanate nanotubes are promising materials for Li-ion battery anodes because of their special morphology and high specific surface areas. These titanates provide high rate capability and low volume expansion upon lithiation. More importantly, their tubular structure helps the transport of ions through the crystal. In this study, we synthesized elongated titanate nanotubes and modified their interlayer distances by changing the pH (2-13). For the structural characterization XRD, BET, SEM and TEM techniques were used. In addition, the effect of interlayer distance on energy capacity and rate capability was investigated. The highest interlayer distance was obtained at pH 10 and with decreasing pH, the interlayer distance dropped until reaching a pH value of 4. Conversely, the specific surface area reached its maximum value of 204 m(2) g(-1) at a pH of 4. Different from anatase (TiO2), titanate nanotubes had broad peaks in cyclic voltammograms suggesting a pseudocapacitive behavior. The sloping profiles of potential-capacity results also supported the pseudocapacitive property. For the titanate nanotubes obtained at pH 10, an initial discharge capacity of 980 mAh g(-1) was achieved. More importantly, titanate nanotubes showed exceptional rate capabilities and the capacities stayed almost constant at high current rates because of their elongated structure. It was found that the interlayer distance and the elongated structure play an important role in the electrochemical performance of the material.