Current Organic Chemistry - Volume 15, Issue 16, 2011

Organosilicon chemistry has a considerable and growing importance both in industry and in the academic world. It is an important subject that draws on and contributes to the traditional areas of organic, inorganic, physical, polymer chemistry and materials. This multidisciplinary application gives a unique strength to organosilicon chemistry. The unabated growth of applications of organosilicon in the resolution of synthetic problems has continued in the last five decades. Especially in the past decades, the synthesis and application of organosilicon compounds are finding important in organic chemistry. This special issue was the occasion to collect the contributions of the researchers working in organosilicon chemistry and organic synthesis in order to provide the progress of organosilicon-mediated organic synthesis at present. I am sure that these contributions collected in the following five reviews will provide extremely useful information and future directions on the topic of organosilicon-mediated organic synthesis. The first review is provided by Prof. Cheng. The use of organosilicon compounds in carbon-carbon and carbon-heteroatom coupling reaction has many advantages in comparison to other organometallic donors due to their ease of handling, stability toward air/moisture, and/or low toxicity compared to some of the other organometallic reagents (Zn, Mg, Sn, etc.). In this review, the authors focused on the application of aryl trialkoxysilane and alkenyltrialkoxysilane as transmetallation reagent for C-C, C-N, C-S and C-O bonds formation, which demonstrated the importance of trialkoxysilane as transmetallation reagent in several important organic transformations. Hydrosilylation of carbon-carbon multiple bonds with hydrosilane catalyzed with transition metal complexes remains the most commercially utilized process for formation of organosilicon compounds and it is a key step for the preparation of alcohols from olefines with the aid of organosilicon compounds. In view of catalytic systems which are the basis and key studies of extensive development of synthetic methodologies concerning hydrosilylation processes of carbon-carbon and carbon-heteroatom multiple bonds, Prof. Peng and Lai focused on the recent progress in transition metal-catalyzed hydrosilylation of carbon-carbon multiple bonds with different hydrosilanes in the second review. The third review is designed by Prof. Yoo to present the progress of different Si-C coupling reactions of hydrosilanes, which will stimulate the use of Si-C coupling reactions in the synthesis of organosilicon compounds. It is revealed that hydrosilane undergoes useful and interesting Si-C coupling reactions with activated organic compounds such as linear and cyclic alkyl chlorides, polychloromethanes, terminal and internal alkenes, and linear and cyclic conjugated dienes to give a variety of organosilicon compounds with Si-Cl units, one of the most important functional organosilicon compounds in organic synthesis. Organosilicon-mediated synthesis of functionalized phosphonic acids is a relatively new area of research. It is interesting that organosilicon compounds act as an unnegligible role in the synthesis of functionalized mono- and bisphosphonic Acids. In the fourth review, Prof. Romanenko presented an overview of new and useful silicon-based methodologies valuable for the selective construction of highly functionalized mono- and bisphosphonic acids of high synthetic and biological importance. It is anticipated that these progess in this context will help researchers to the discovery of novel highly efficient method for the synthesis of organophosphorus compounds. As a class of conventional reagents of low cost and easy availability, it is well-known that organosilicon compounds have been explored with abundant utilities in organic reaction, such as Michael/aza-Michael reaction, conjugate addition, Mannich reaction, and many important carbon-carbon and carbon-heteroatom bond-forming reactions. Many organosilicon compounds such as TMSCl, TMSI, TMSOTf etc. have been endowed with unique functions compared with analogous catalysts in these reactions, such as strong Lewis acidity and good chelation with carbonyl compounds. However, the organosilicon compounds mediated multicomponents reactions is overlooked in some extent. In the fifth review, Dr. Wan summaried the recent progress of Multicomponents reactions (MCRs) employing organosillicon reagents as catalysts or promoters. The achieved progress in this field inidcates that the development of efficient organosilicon-mediated MCRs is highly desired and would be a promising research topic in the next decades due to the diversity of MCRs and organosilicon compounds with special identities of silicon element. Finally, as a Guest Editor for this special issue, I would like to thank all the authors contributing to this special issue for their valuable work. I hope that the overall effort will provide inspiration to modern organic chemsitry and organosilicon chemistry to creat new challenges and promising achievements of organosilicon-mediated organic synthesis in the future.

Hydrosilane undergoes useful and interesting Si-C coupling reactions with activated organic compounds such as linear and cyclic alkyl chlorides, polychloromethanes, terminal and internal alkenes, and linear and cyclic conjugated dienes to give a variety of organosilicon compounds with Si-Cl units: 1) thermal induced and Pt-catalyzed hydrosilylation reaction with unsaturated organic compounds, 2) organic salt-catalyzed dehydrochlorinative Si-C coupling reaction with alkyl chlorides, 3) double silylation with olefin, and silylene-trapped ring closure reaction with conjugated dienes. In the quaternary phosphonium chloride-catalyzed dehydrochlorinative Si- C coupling reactions of activated organic compounds with HSiCl3, the reaction with relatively activated allyl chloride and benzyl chloride proceeded at 130 °C to give the corresponding coupling products in good to excellent yields, while that of silylalkyl chlorides and primary/ secondary alkyl chlorides required high reaction temperatures of 150 °C and 170 °C, respectively and long reaction times. Reaction with olefin at the high temperature of 180 °C gave double silylation product in good yield. Conjugated dienes reacted with 1a at 150 °C to afford 1,1-dichlorosilacyclopent-3-ene. This review is designed to organize the Si-C coupling reactions into categories that illustrate distinct patterns of reactivity. It is hoped that an understanding of such patterns will stimulate the use of Si-C coupling reactions in the synthesis of organosilicon compounds.

Organosillicon reagents have been found as versatile catalysts or promoters for a broad range of organic reactions due to their special properties of multifunction. An important application of organosilicon reagents is in the research field of multicomponent reactions (MCRs), which provides a vast number of practical synthesis for different molecular libraries. We present in this review the recent research progress of MCRs employing organosillicon reagents as catalysts or promoters for the first time.

The aim of this article is to present an overview of new and useful silicon-based methodologies valuable for the selective construction of highly functionalized mono- and bisphosphonic acids of high synthetic and biological importance. The reactions of trimethylsilyl phosphites with alkyl halides, carbonyl compounds and imines are presented as a platform for developing new approaches to biologically active hydroxy-, amino-, fluoro-substituted mono- and bisphosphonates. The second part of the review consists of a presentation of methodology involving the fluoride-induced formation of -phosphonylated carbanions from 1-trimethylsilyl methylphosphonates. The third part of the review describes the methodology employing silylated phosphonate carbanions. Application of trimethylsilyl as protecting group is discussed in separate section.

Recent progress in the catalytic hydrosilylation of organic compounds containing carbon-carbon multiple bonds is reviewed. Hydrosilylation of carbon-carbon multiple bonds catalyzed with transition metal complexes remains the most commercially utilized process for formation of organosilicon compounds. During the last two decades, a number of simple and versatile catalytic systems including homogenous and heterogenous systems and even those for asymmetric catalysis procedures have been developed. These transition metal catalysts increased catalytic efficiency as well as regioselectivity and stereoselectivity.

Organosilicon compounds are important transmetallation reagents in organic synthesis. Aryltrialkoxysilane have recently emerged as an attractive alternative to traditional organometallic donors, due to their ease of handling, stability toward air/moisture, and/or low toxicity compared to some of the other organometallic reagents (Zn, Mg, Sn, etc.). In this review, the application of aryl trialkoxysilane and alkenyltrialkoxysilane as transmetallation reagent for C-C, C-N, C-S and C-O bonds formation will be disclosed.

The last decade has witnessed a tremendous increase of the studies concerning [3+2] cycloaddition reactions of azides and alkynes. The recent discovery of copper(I) species as efficient catalysts for this transformation is at the origin of this true explosion. In contrast with classical thermal reactions, copper catalysis leads to the regioselective formation of 1,4-disubstituted 1,2,3-triazoles in high yields and under simple reaction conditions. This transformation has indeed become the most prominent example of the principles of Click chemistry, postulated in 2001 by Sharpless and co-workers. Despite the ever-increasing interest in this process, the use of ligands in this context remains minor when compared to ligandless systems. Nevertheless, besides overcoming the inherent limitations of ligandless systems, the use of ligands in this context has been shown to increase and, more importantly, modulate the catalytic activity of the metal center. Herein, the catalytic activities of ligated copper systems are reviewed in a way intended inspirational for future developments in this field.

Tri-substituted oxazoles, appearing in several anticancer natural products and various other bioactive compounds, have become increasingly visible in recent years. Research into the synthesis of such oxazoles has led to the development of new synthetic methods as well as refinements of classic methods of their synthesis. In addition, a number of research groups have pursued the synthesis of fully-functionalized-oxazole-containing natural products. We review recent investigations (2004-present) into methods of tri-substituted oxazole synthesis, and the construction of complex natural products containing such oxazoles.

The family of cisplatin and its analogues contains some of the most powerful anticancer drugs developed to date and, since their discovery, extensive efforts have been devoted to understand their mode of action. 9-Alkylguanines have featured widely in these studies as model nucleobases. This review describes both the synthesis and the chemical, biological and miscellaneous spectroscopic properties of a variety of transition metal ion (Pt, Pd, Ru, Os, Rh, Re, Tc, Zn, Cu, Cd) complexes of N-alkylguanines (mostly 9- alkylguanines) which have been reported in the literature principally within the 2003-2008 period. Special attention has been given to the acid-base properties of these complexes, where coordination to transition metal ions usually leads to significant acidification of the guaninyl N1-H proton, and its consequences

In the study of thioanhydrides, a fast, simple, and cost effective means of producing thioanhydrides is necessary being that commercially available thioanhydrides are limited. A simple method of converting an anhydride into a thioanhydride involves the use of sodium sulfide. In general, this method of thioanhydride synthesis is effective in producing a substantial yield of thioanhydride from the conjugate anhydride. However, in the case of itaconic anhydride, this method seems to fail. By monitoring the reaction of itaconic anhydride with sodium sulfide using 1H NMR spectrometry, Raman spectrometry, and IR spectrometry, it is clear that the resulting product is not the expected itaconic thioanhydride, but is instead citraconic anhydride, an isomer of itaconic anhydride. While this isomerization reaction has been recorded using nitrogen-based compounds, this is the first instance in which sodium sulfide has been recorded as a catalyst in the isomerization of itaconic anhydride to citraconic anhydride.

This review article summarizes progress in N-alkylations, N-alkenylations, N-and C-arylations and hetarylations, halogenations, as well as organometallic chemistry of pyrazoles mainly achieved during the last decade. In addition, the generation and chemistry of N-heterocyclic carbenes of pyrazole (pyrazol-3-ylidenes) and remote N-heterocyclic carbenes of pyrazole (pyrazol-4-ylidenes) are described.