Current Organic Chemistry - Volume 20, Issue 27, 2016

The generation of perfluoroalkyl radicals (RF•) by means of photocatalysis is a more suitable route than the established methods employing chemical initiators, like azo or peroxide compounds or the use of transition metals. Conditions governed by photocatalysis can allow for a wide range of functional groups and, therefore, can be applied to the latestage transformation of bioactive molecules. Organic photocatalysts (POC), in the absence of transition metals, can suffer electron-exchange reactions, yielding RF radicals. RF radical production without the assistance of transition metals through the employment of POC will be described, applying this methodology to studying classical examples.

Five-membered ring products of cyclometalation reactions are utilized as dyesensitizers for manufacturing very stable dye-sensitized solar cells. Such solar cells have greater stability than standard chelate-type N719 solar cells because the cyclometalated ligands in the five-membered ring products are stronger donors than the thiocyanate groups in the standard type. Solar cells with high overall energy conversion efficiencies are manufactured primarily by using three types of cyclometalated five-membered-ring ruthenium compounds: 1. A solar cell prepared with a phenylpyridine ruthenium compound, e.g., bis(4,4'-dicarboxy- 2,2'-bipyridine) 2-(2,4-difluorophenyl)pyridine ruthenium, shows an overall energy conversion efficiency of 10.1 %. 2. A solar cell with the ruthenium compound with 2,2’-bipyridine bearing two carboxyl ligands and two alkylthienothophene ligands and 2,3’-bipyridine bearing two alkyloxy ligands shows a high overall energy conversion efficiency with 9.4 % with the cobalt electrolyte [Co(phen)3]3+/2+. 3. A solar cell using a clometalated CNN tridentate ruthenium compound bearing an electron-donating substituent of a terminal substituent placed para to the triphenylamine achieves a high overall solar-to-electric energy conversion efficiency of 8.02 %. This result is almost the same as that of N3 under the same conditions.

During the last decades, indium chemistry has attracted considerable attentions from synthetic community and has found widespread applications in organic synthesis. Compared to many other commonly used metals (such as Li, Al, Mg, and Zn), indium is insensitive to water and air, allowing the operation of indium-mediated organic transformations in aqueous media. In addition, its mildness also permits indium-mediated reactions to proceed with better functional group tolerance and sometimes better chemoselectivity. In this review, a wide variety of the applications of indium in organic synthesis are summarized, with a special emphasis on reactions which have been reported recently, such as allylation reaction, alkylation reaction, cross-dehydrogenative coupling (CDC), aldehyde and enone cross-coupling reaction, Prins-type cyclization, radical cyclization, propargylation/allenylation of imines, and Diels-Alder reaction.

In this study, we want to have an extensive overview on the application of triphosgene in organic synthesis. We begin with an introductory discussion of the nature of triphosgene, and introduce several procedures for the preparation of triphosgene. It holds an advantage over other similar reagents, such as phosgene and diphosgene, of being a safe and easy to handle solid. On the other hand, it is safer and more convenient to transport and store. Exact amounts may be weighed easily and used to perform desired chemical transformations and reaction requires only one-third equivalent of triphosgene in most cases. We then survey the reactions and transformations that performed using triphosgene. The reactions have been performed using triphosgene are carried out under mild conditions and afford good to excellent yields. The use of triphosgene as a synthetic auxiliary in the preparation of many important classes of organic compounds has been investigated intensively in the last years. Finally, we summarize the advantages of triphosgene in organic synthesis.

At present, ionic liquids (ILs) are playing a more and more important role in organic synthesis as green catalysts and solvents. At the same time, researchers from both academia and industry have great interests in the related application of new ILs with unique structural features. Many neutral and acidic ionic liquids were used to catalyze condensation and esterification processes, which are two important reactions in fine chemical, material, energy and pharmaceutical industry. Compared with traditional catalysts, these ionic liquids have shown special advantages and potential due to their ideal catalytic performance and the unusual characteristics. For instance, temperature-sensitive ILs can automatically form a liquid-solid two phase system so it can be recovered easily from the reaction system after the synthetic process is completed, and the advantages of heterogeneous and homogeneous catalysis can be achieved simultaneously. On the basis of our recent study and latest development, the paper reviews the current application and related catalysis mechanism of ILs in above reactions in detail, especially for those with new structures. Moreover, the development trend and challenges in the further use of ILs are also discussed. It is expected to provide meaningful reference for involved researchers.

Both carbonyl groups of a β-keto amide are highly activated by intramolecular hydrogen bonding. Hence, β-keto amides readily undergo amination, giving either β-aminobutenamides or N-substituted acetoacetamides. The chemoselectivity was influenced by the steric bulk of the keto amide or the amine: while amination at the ketone moiety predominated at low temperatures with less hindered substrates, amination at the amide moiety occurred at higher temperatures with sterically hindered substrates. In addition, a β-aminobutenamide with a bulky amino group was converted to an N-substituted acetoacetamide by simply heating to a high temperature. Based on the experimental results, as well as density functional theory (DFT) calculations, N-substituted acetoacetamides were more stable than β-aminobutenamides when the amino group is bulky. This reaction allows the direct synthesis of N-substituted acetoacetamides from N-unsubstituted acetoacetamides.

In 1893, the synthesis of 3,4-dihydropyrimidin-2(1H)-ones via three-component condensation reaction of an aromatic aldehyde, urea and ethyl acetoacetate was reported for the first time by P. Biginelli. In the past century, such 3,4-dihydropyrimidin-2-(1H)-ones and related heterocyclic compounds have received a considerable amount of attention due to the interesting pharmacological properties associated with this heterocyclic scaffold. In particular, in recent twenty years, the synthesis of functionalized 3,4-dihydropyrimidin-2(1H)-ones have made great breakthrough. However, the asymmetric synthesis of functionalized 3,4-dihydropyrimidin-2(1H)-ones catalyzed by organocatalysts also is less. Furthermore, the 6-isopropyl dihydropyrimidines are very important intermediates for Statin drug. In this article, we mainly developed a simple and practical scheme for the synthesis of 6-isopropyl-3,4-dihydropyrimidines in a one-pot three-component condensation of aldehydes, β-dicarbonyl compounds, and thiourea via organocatalyzed asymmetric Biginelli reaction. Under the optimal reaction conditions, a series of desired products with remarkable pharmacological interest was obtained in high yields with excellent enantiomeric excess (up to 99% ee) using this practical method.

Nowadays, biodegradable polymers are attractive candidates to create highperformance and environmentally friendly catalytic species. Polymeric materials for catalytic processes must be biocompatible and preferably biodegradable. Sulfonic acid functionalized chitosan (CS-SO3H) was easily prepared by the reaction of chitosan with chlorosulfonic acid. CS-SO3H is found to catalyze the Hantzsch reaction to produce 1,4-dihydropyridines (1,4DHPs) via the condensation reaction of aldehydes, ethyl acetoacetate and ammonium acetate with high efficiency. The use of heterogeneous and biodegradable CS-SO3H makes this synthetic methodology quite simple, more convenient and economically viable compared to homogeneous chitosan catalyzed method. CS-SO3H with nanopore structure, with encapsulated reactants may be applied as a nanoreactor for this chemical reaction. The main advantages of this protocol are the eco-friendly catalyst system, heterogeneous nature, freedom from organic solvents, and ease of the workup procedure. The present method can be used for the green design of heterocyclic compounds, and has potential for biological applications and drug discovery.