Current Organic Chemistry - Volume 15, Issue 5, 2011

When my proposal of a special issue entitled “Recent Progress in the Synthesis and Applications of Cyclic Compounds” for Current Organic Chemistry was approved by the Editor-in-Chief of the journal in February 2009, I was very happy to start the edition of this special issue that I immediately released a call for manuscripts on my laboratory's website (http://chem.tsinghua.edu.cn/huarm/) and sent about 30 invitation letters to potential authors. A month later, nearly 15 authors agreed to make a contribution for this special issue. Finally, 10 papers from different universities and institutes with authors hailing from 10 countries were selected for publication with respect to different themes in the synthesis and applications of cyclic compounds. This special issue involves topics concerning the synthesis and applications of bismuth-containing heterocyclic compounds contributed by Dr. S. Shimada (National Institute of Advanced Industrial Science and Technology (AIST), Japan), applications of carbon dioxide in the synthesis of heterocyclic compounds summarized by Dr. L. He and coworkers (Nankai University, China), recent developments in the synthesis and application of three- and four-membered heterocycles written by Dr. B. Myrboh and co-workers (North Eastern Hill University, India), recent advances in the regioselective synthesis of pyrazoles reviewed by Dr. H. Shin and co-workers (LG Life Sciences, Ltd./R & D, Korea), synthesis of five-membered sulfur-heterocycles via 1,5- dipolar electrocyclization of thiocarbonyl ylides and related processes reviewed by Drs. G. Mloston and H. Heimgartner (University of Lodz, Poland and University of Zurich, Switzerland), recent advances in the synthesis of five-membered heterocycles contributed by Dr. S. Hameed and T. Akhtar (Quaid-I-Azam University, Pakistan), recent achievements in the chemistry of 1,2-diazines written by Dr. I. I. Mangalagiu (“Al. I. Cuza” University of Iasi, Romania), recent progress in the synthesis and applications of heterocycles derived from enaminonitrile revieweded by Dr. S. Bondock and co-workers (Mansoura University, Egypt), isocoumarin and its derivatives: an overview on their synthesis and application, contributed by Dr. S. Pal and co-workers (MNR Degree and PG College, India), and cycloaddition of alkynes: atom-economic protocols for constructing six-membered cycles, submitted by myself, with co-authors Miss Maria Victoria A. Abrenica (Wellesley College, USA) and Ping Wang (Tsinghua University, China). Although only 10 review papers are included in this special issue, more than 500 reactions are described and over 1100 literature references are cited. I believe this issue has a comprehensive coverage of important and up-to-date reactions for the synthesis of cyclic compounds and their applications in organic synthesis. As guest editor, I would first like to acknowledge all the authors who have made contributions to this special issue. I deeply thank all the referees for their exceedingly helpful comments on improving the quality of the manuscripts. I wish to express a special thanks to Miss Maria Victoria A. Abrenica, one of the authors in this special issue, for her help in proofreading all the manuscripts. Finally, a huge thanks to Dr. Atta-ur-Rahman, Editor-in-Chief of Current Organic Chemistry for his kind invitation to me to edit this special issue as guest editor, and to Dr. D. Akhter, assistant manager of the publication department at Bentham Science Publishers, for her kind communications throughout the whole process of editing. I look forward to a fruitful cooperation with you all again in the near future! This special issue is dedicated to the occasion of the 100th anniversary of Tsinghua University in 2011.

This review overviews the advances in the chemistry of bismuth-containing heterocyclic compounds during the last decade. Some new types of bismuth-containing heterocyclic systems containing nitrogen, oxygen, sulfur and/or phosphorus in addition to bismuth have been synthesized. 5,6,7,12-Tetrahydrodibenz[c,f][1,5]azabismocine derivatives were the most extensively studied bismuthcontaining heterocyclic compounds during the last decade, and a number of new compounds were synthesized. Their application to organic synthesis has shown that they are useful as reagents for the cross-coupling reaction with organic halides and as Lewis acid catalysts. Also they were used for the fixation of CO2. Some pentavalent bismuth-containing heterocyclic compounds were found to be useful in organic synthesis. Biological activity of some of bismuth-containing heterocyclic compounds was studied and found to show antimicrobial, antibacterial, antifungal, and anticancer activities.

As an abundant, nontoxic, nonflammable, easily available, and renewable carbon resource, carbon dioxide is very attractive as an environmentally friendly feedstock for making commodity chemicals, fuels, and materials. Owing to its kinetic and thermodynamic stability, significant efforts have been directed towards constructing C-C, C-O and C-N bond on the basis of CO2 activation through molecular catalysis. Development of catalytic methodologies for chemical transformation of CO2 into useful compounds is of paramount importance from a standpoint of C1 chemistry and green chemistry. The aim of this review is to demonstrate the versatile use of CO2 in heterocyclic synthesis, with the main focus on utilization of CO2 as a building block for synthesis of five- and six-membered heterocyclic compounds such as cyclic carbonates, oxazolidinones, imidazolidinones, lactones, quinazolines, etc. The potential use of dense CO2 as an alternative solvent and otherwise specific roles in the heterocyclic synthesis are also evaluated. We hope this presentation will stimulate further interest in research that may pave the way for selective synthesis of heterocycles employing CO2 as a synthon.

This review aims at giving a brief summary on the preparation of three and four membered heterocycles laying particular emphasis on the various green approaches for the synthesis of substituted aziridines, thiiranes, β-lactams, diones and thietanes. The review presents the result of our literature survey of the work done in recent years on the use of solid support catalyzed reaction and more environmentally benign approaches for three and four membered heterocyclic synthesis.

Pyrazole is the ubiquitous sub-structure of many natural products and biologically active compounds. In this respect, its regioselective synthesis drew a lot of attention from synthetic organic chemists, leading to the development of various regioselective modifications of the classical Knorr cyclocondensation reaction and alternative methods. This review covers the period of 2003 to the middle of 2009 on the regioselective synthesis of pyrazoles, which are categorized into four reaction types: (i) modified Knorr condensation reaction using 1,3-dicarbonyl surrogates; (ii) 1,3-dipolar cycloadditions approach; (iii) regioselective direct substitution reaction of the pyrazole ring system; and (iv) other methods.

The reactive thiocarbonyl ylides belong to the less well-known class of the so-called ‘sulfur-centered 1,3-dipoles’. Only in recent years have the [2+3] cycloadditions with thiocarbonyl ylides been extensively explored, mainly as a useful method for the synthesis of three- and five-membered sulfur heterocycles. The goal of the present review is to demonstrate the potential of the 1,5-dipolar electrocyclization of properly substituted thiocarbonyl ylides as an alternative approach to syntheses of sulfur heterocycles such as 1,3- oxathiolanes, 1,3-thiazoles, 1,3-dithioles, and thiophenes. Thermal, as well as metal-catalyzed, generations of the reactive intermediates from diazo and thiocarbonyl precursors are summarized and discussed. The presented examples show the scope and limitations of this general but relatively scarcely-investigated reaction.

Five-membered heterocycles are very important from the synthetic aspect because of their enormous pharmacological applications. Several new reagents, substrates and methods are being developed every year to facilitate their synthesis. This review is an effort to sum up the methods recently utilized in the synthesis of this important group of heterocycles.

Recent advances on the synthesis of six-membered carbo- and heterocyclic compounds including functionalized benzenes, 1,3- cyclohexadienes, pyridines, pyridones, pyranones, coumarins and isocoumarins via the cycloaddition reaction of alkynes are reviewed. Special attention is paid to atom-economic controllable chemo- and regioselective reactions, which are currently extremely attractive methodologies in organic synthesis.

Recent studies have centred on 1,2-diazines derivatives, which proved to be invaluable materials in the fields of medicine, opto-electronics and agriculture. 1,2-diazines were found to have pharmaceutical applications including a wide range of biological activities, such as antiviral and anticancer, antituberculosis, antimicrobials, antifungus, anti-inflammatory, antihypertensive, diuretics, antithrombics, anticoagulants, antidepressant, anxiolytics, anticonvulsant, analgesic, and anti-multiple sclerosis. Their applications in the field of electronics are mainly focused on highly fluorescent derivatives (with potential as sensors and biosensors, electroluminescent materials, lasers, and other semiconductor devices) and compounds with liquid crystal properties. Herbicidal activity and the grow up factor for plants are also reviewed. Microwave assisted organic synthesis (MAOS) has during the last years become an invaluable tool within chemistry research, which has shown to be a very efficient way towards the synthesis of many compounds. In this review, microwave assisted reactions of 1,2-diazine derivatives have been discussed, outlining an introduction to MW chemistry, N-alkylations, dipolar cycloadditions, cyclocondensations, transition-metal catalysed reactions, and nucleophilic substitution of 1,2- diazines.

Recent progress in the synthesis and use of enaminonitriles as precursors for carbocyclic and heterocyclic compounds is reviewed. The synthetic routes for preparation of enaminonitriles are based on addition and condensation reactions. Enaminonitriles can be used as building blocks for carbocyclic, five, six, and seven-membered heterocycles as well as fused heterocyclic compounds. Biological and industrial applications of heterocycles derived from enaminonitriles are also discussed.

The prevalence of isocoumarins in numerous natural products that exhibit a wide range of biological activities has generated a continued and enormous interest among synthetic and medicinal chemists. The isocoumarin framework represents one of the privileged structures for the development of natural product-inspired compounds of potential biological interest. Considerable efforts have been devoted towards the synthesis of isocoumarins via either traditional or transition-metal catalyzed reactions. Among the metal catalyzed reactions, the use of Cu, Pd, Ag, Ru, Rh or Ir salts/complexes for the construction of isocoumarin ring are noteworthy. Among the other methodologies, halo-lactonization emerged as a practical process. Apart from preparing a variety of isocoumarins and thienopyranones, synthesis of naturally occurring and bioactive isocoumarins have been carried out by using cutting edge technologies. This review article will briefly cover all these aspects along with the synthetic utility of isocoumarins, highlighting recent developments.