Current Organic Chemistry - Volume 18, Issue 6, 2014

The cyclopentane carbocyclic ring system, while ubiquitous in nature, is not usually considered a privileged core structure for the development of a drug candidate due, in part, to a perceived synthetic intractability of stereochemically complex target molecules. In this review, we demonstrate that the cyclopentane motif has been utilized as an effective core scaffold for several highly successful medicinal chemistry programs and, thus, has provided an underappreciated yet significant value for biomedical research. Moreover, the modern synthetic methods highlighted in this work offer a wealth of attractive and accessible technologies for the stereocontrolled construction of exceedingly complex cyclopentanoid chemotypes of natural and unnatural origin. We contend that the cyclopentane framework should be regarded as a privileged scaffold for drug discovery research and that expanded screening campaigns of novel cyclopentane- based small molecule libraries for therapeutically relevant biological properties will have a favorable impact on the development of the active pharmaceutical ingredients (APIs) of tomorrow.

Biginelli reaction is the most classical and frequently employed method for facile and diverse synthesis of 3,4- dihydropyrimidinones and thiones (DHPMs)-a class of privileged heterocyclic scaffolds possessing meritorious biological and pharmacological functions. Owing to the presence of a chiral centre in DHPMs and the discovered distinction in biological activity of DHPMs isomers, accessing chiral DHPMs of optical purity constitutes a core issue of particular importance in the research of Biginelli reaction. Following the rapid progress of modern organic synthesis, catalytic asymmetric Biginelli reaction has gradually evolved as the mainstream method instead of early kinetic resolution for acquiring enantiomerically enriched. In the present paper, the advances in catalytic asymmetric Biginelli reaction, including advances in metal catalysis as well as organocatalysis, are comprehensively reviewed.

N-Heterocyclic carbenes (NHCs) as versatile nucleophilic organocatalysts have been extensively studied and also widely applied in organic reactions. The types of organic reactions catalyzed by N-heterocyclic carbenes are broad including benzoin condensation, Stetter reaction, a3-to-d3 umpolung, ring-opening reaction, transesterification, and ring expansion polymerization. This review reports recent developments in the synthesis of heterocycles (such as lactams, lactones, chromones, and benzofuranones) catalyzed by N-heterocyclic carbenes.

High efficiency in the organic synthesis makes the multicomponent reaction (MCR) an attractive research field, in which some three-component reactions such as the Strecker (found in 1850), Hantzsch (1882), Biginelli (1891), Mannich (1912), and Passerini (1921) were widely spread, followed by the findings of some four-component reactions such as the Bucherer Bergs and Asinger reactions found in 1929 and 1956, respectively. However, the reaction among ketone, amine, isonitrile, and carboxylic acid to form bisamide found by Ivar K. Ugi in 1959 still takes the most important position in the MCRs because the Ugi four-component reaction (Ugi 4CR) occurs among four organic reagents in methanol or other popular solvents without the aid of any catalysts. Thus, Ugi 4CR represents a selfresembling process among organic reagents and therefore implies the possibility that an organic reaction may involve more than four reagents within one pot operation. Thus, Ugi 4CR can be regarded as the breakthrough in the research of MCRs. Many published reviews summarize the Ugi 4CR from different viewpoints, but the aim of the presented review on Ugi 4CR together with Passerini three-component reaction (Passerini 3CR) is to introduce a successful mode for the study on MCRs, in which the research on a MCR may involve four aspects including mechanism, substrate, catalyst, and application. The quantum calculation on the energy variation of Ugi 4CR reveals that the addition of isocyanide to imine controls the reaction rate of Ugi 4CR, and imine is generated via the reaction between the amine and ketone at the first step in Ugi 4CR. As a result, the investigation on the substrates of Ugi 4CR focuses on the formation of imine and the resources of carboxylic acid and ketone. Moreover, some catalysts are employed to induce the diastereoisomer ratio because a chiral center is involved in the product of Ugi 4CR. In addition, Lewis acid is used to activate the inert reagents or to drive the further reactions based on Ugi 4CR products. The application of Ugi 4CR is not the major concern in this review because many previous reviews have focused on this topic. Only some recently published results are documented herein. For example, Ugi 4CR can be used to construct macromolecules with complicated topological structure, to introduce medicinal molecule into nanoparticles, and to synthesize biological-related molecules. Finally, a successful model for the research on MCR can be summarized from the study on Ugi 4CR. Understanding mechanism is the basis for investigating MCR, followed by expanding the suitable substrates and exploring the chiral catalysts. As a result, the MCR can be widely applied to synthesize various molecules.

Organic fluorophores have at times been criticized for their wide band emission. In the rapidly developing field of white lightemitting devices (WOLEDs) however, such features have become exalted in the search for dyes that display panchromatic emission. To achieve white light emission, mixing of emitters that emit red, green and blue (RGB) or complementary color mixing of bluish/green with orange/red colors represent the most common methods. Among the various design approaches, single white-light emitters feature improved stability, better reproducibility, and true single-chromophore layer fabrication. The intent of this review is to inform promising researchers of the fundamental requirements for single-emitter chromophore design and present the latest developments obtained through different research directions. Thus, molecular systems with the unique capacity to emit white-light are categorized into small organic molecules, dendrimers, polymeric molecules, and organometallic complexes. These single white-light emitters groups are further classified as either photoluminescent (in solution or thin films) or electro-luminescent (EL). In addition to providing examples of the authors’ contributions to the field, the review provides a brief outline of the synthetic routes for certain white-light emitters. Where possible, a description of the photophysical properties is given as well as commentary on the white-light emitter features such as excitation and emission wavelength maxima within each class of compounds. Therefore, strategies to obtain new white light emitters including thin film requirements, CIE index values and turn-on voltage for electroluminescent systems are summarized for those seeking to contribute to the leading emerging technology in display devices.