Tosylhydrazones: new uses for classic reagents in palladium-catalyzed cross-coupling and metal-free reactions

Tosylhydrazones are useful synthetic intermediates that have been used in organic chemistry for almost 60 years. The recent discovery of a palladium-catalyzed cross-coupling reaction involving a tosylhydrazone coupling partner has triggered renewed interest in these reagents. This reaction shows nearly universal generality with regard to the hydrazone and can be employed for the preparation of polysubstituted alkenes. In the course of this research, novel metal-free C-C and C-O bond-forming reactions have been discovered. Since tosylhydrazones are readily prepared from carbonyl compounds, these transformations offer new synthetic opportunities for the unconventional modification of carbonyl compounds. This Minireview discusses all of these new reactions of a classic reagent.     

The thriving chemistry of ketenimines

Ketenimines are an important class of reactive species and useful synthetic intermediates. During the last two decades several practical and versatile approaches to ketenimines have been developed, leading to exhaustive investigations on ketenimine chemistry and the discovery of a variety of highly efficient reactions. Five types of reactions for ketenimines have been reported, including nucleophilic additions (ketenimines can be used as both electrophiles and nucleophiles), radical additions, cycloaddition reactions, electrocyclic ring closure reactions, and σ rearrangements. Furthermore, numerous complex organic compounds, particularly the biologically interesting heterocycles, have been constructed using these methodologies. The review of these accomplishments is presented here.     

Synthesis of naturally occurring polyynes

Over the past fifty years, hundreds of polyyne compounds have been isolated from nature. These often unstable molecules are found in sources as common as garden vegetables and as obscure as bacterial cultures. Naturally occurring polyynes feature a wide range of structural diversity and display an equally broad array of biological properties. Early synthetic efforts relied primarily on Cu-catalyzed, oxidative acetylenic homo- and heterocoupling reactions to assemble the polyyne framework. The past 25 years, however, have witnessed a renaissance in the field of polyyne natural product synthesis: transition-metal-catalyzed alkynylation reactions and asymmetric transformations have combined to substantially expand access to natural polyynes. This Review recounts these synthetic achievements and also highlights both the natural source(s) and biological relevance for many of these compounds.     

Catalytic Asymmetric Hetero-Diels-Alder Reactions of Carbonyl Compounds and Imines

Asymmetric catalysis is a challenge for chemists: How can we design catalysts to achieve the goal of forming optically active compounds? This review provides the reader with an overview of the development of catalytic asymmetric hetero-Diels-Alder reactions of carbonyl compounds and imines. Since its discovery, the Diels-Alder reaction has undergone intensive development and is of fundamental importance for synthetic, physical, and theoretical chemists. The Diels-Alder reaction has been through different stages of development, and at the beginning of the 21st century catalytic Diels-Alder reactions are one of the main areas of focus. The preparation of numerous compounds of importance for our society is based on cycloaddition reactions to carbonyl compounds and imines. There are several parallels between the reactions of carbonyl compounds and those of imines, which, however, begin to vanish on entering the field of catalytic reactions. Why? From a mechanistic point of view some similarities can be drawn, but the synthetic development of catalytic enantioselective hetero-Diels-Alder reactions of imines are several years behind those of the carbonyl compounds. For hetero-Diels-Alder reactions of carbonyl compounds there a number of different chiral catalysts, and great progress has been achieved in developing enantioselective reactions for unactivated and activated carbonyl compounds. In contrast the development of catalytic enantioselective hetero-Diels-Alder reactions of imines is in its infancy and only few catalytic reactions have been published. This review will focus on the most important developments, and discuss the synthetic and mechanistic aspects of enantioselective hetero-Diels-Alder reactions of carbonyl compounds catalyzed by chiral Lewis acids. For the hetero-Diels-Alder reactions of imines, the diastereoselective reactions of optically substrates catalyzed by Lewis acids will be presented first, followed by the catalytic enantioselective reactions.     

Catalytic asymmetric synthesis of alpha- and beta-amino phosphonic acid derivatives

Catalytic asymmetric reactions provide one of the most powerful and economical synthetic approaches to a variety of enantiomerically enriched compounds. As being analogues of the corresponding alpha- and beta-amino acids, optically active alpha- and beta-amino phosphonic acid derivatives have found widespread use in medicinal chemistry and the pharmaceutical sciences. Using catalytic amounts of chiral materials, asymmetric synthesis of enantiomerically enriched alpha- and beta-amino phosphonates has been a subject of growing interest. This tutorial review contains a compilation of the catalytic asymmetric synthetic methods developed to date and highlights their utility for obtaining these target compounds.     

Intramolecular cross-dehydrogenative coupling of benzaldehyde derivatives: A novel and efficient route to benzocyclic ketones

Benzocyclic ketones are not only found throughout many natural products and synthetic pharmaceutically active compounds but also used as versatile building blocks in organic synthesis. In view of their importance, many researchers have been working to explore novel and efficient synthetic routes for this class of carbonyl compounds. Recently, cross-dehydrogenative coupling reactions have emerged as one of the most versatile and powerful synthetic strategies to construct various carbon-carbon and carbon-heteroatom bonds. In this regard, direct acylation of (hetero)arenes with aldehydes through C(sp²)-H activation opened up a new page on the synthesis of the titled compounds. In this focus-review, we discuss the most representative and important reports on the synthesis of cyclic diaryl ketones through intramolecular cross-dehydrogenative coupling reactions of corresponding benzaldehydes with emphasis on the mechanistic aspects of the reactions.     

Development of a catalytic enantioselective synthesis of the guanacastepene and heptemerone tricyclic core

For nearly two decades, synthetic chemists have been fascinated by the structural complexity and synthetic challenges afforded by the guanacastepene and heptemerone diterpenoids. Numerous synthetic approaches to these compounds have been reported, but to date the application of enantioselective catalysis to this problem has not been realized. Herein we report an enantioselective synthesis of an advanced intermediate corresponding to the tricyclic core common to the guanacastepenes and heptemerones. Highlights of this work include sequential Pd-catalyzed decarboxylative allylic alkylation reactions to generate the two all carbon quaternary stereocenters, the use of ring-closing metathesis to close the A ring in the presence of a distal allyl sidechain, and a regio- and diastereoselective oxidation of a trienol ether to introduce oxygenation on the A ring.     

A study of the copper-catalysed direct arylation of β-dicarbonyl compounds with 2-bromobenzoic acids

The Cu-catalysed condensations of 2-bromobenzoic acids with β-dicarbonyl anions to give α-arylated-β-dicarbonyl compounds have been investigated in detail. Previously recommended experimental conditions for these reactions are shown to be in appropriate and the limited synthetic utility of these processes in the past is explained. Much superior conditions have now been developed by use of which a variety of β-dicarbonyl compounds can readily be arylated in good to excellent yield with A wide range of substituted 2-bromobenzoic acids and with certain other halo-aromatic acids. The scope and limitations of the synthetic method have been established, and a simple, high yield procedure for the preparation of homophthalic acids is described. It is shown that Cu(I) is almost certainly the effective catalyst, and information has been obtained on the probable mechanism of the substitution reaction by examination of steric and electronic effects in the halo-aromatic acids and by consideration of the structure and role of the β-dicarbonyl component.     

Hydroalumination reactions on acetylenes and nitriles in the synthesis of carbaalanes and imidoalanes: an overview

Hydroalumination reactions play an important role in industry as well as from the point of view of academics. The area of carbaalane chemistry is in its infant stage whereas aluminium nitride chemistry has generated a lot of interest from the synthetic and material science perspective. In this overview, we address the simple way of carrying out the hydroalumination reactions on acetylenes and nitriles in the synthesis of carbaalane and imidoalane cluster compounds. A possible mechanism involved in the synthesis of these compounds is discussed. Heteronuclear carbaalane and imidoalane clusters containing transition metals have also been emphasized.     

手性催化的环氧化物立体选择性开环反应

手性催化的环氧化物立体选择性开环反应可以用来制备多种具光学活性的化合物, 因而成为有机合成中极为重要的方法之一. 多种亲核试剂都已成功应用于此类反应. 综述了近十年来环氧化物的立体选择性开环反应方面的一些最新研究进展.     

Benzhydryldimethylsilyl allylic silanes: syntheses and applications to

A new silyl group, the benzhydryldimethylsilyl group, has been developed that is easily synthesized and that undergoes facile oxidation. The [3 + 2] annulation reactions of allylic silanes with this silyl group provide a variety of highly substituted five-membered carbocycles and heterocycles with high stereoselectivities. The silyl groups of these cyclic compounds have been oxidized to hydroxyl groups to demonstrate the general synthetic utility of the method.     

Dinitroso and polynitroso compounds

The growing interest in the chemistry of C-nitroso compounds (RN=O; R = alkyl or aryl group) is due in part to the recognition of their participation in various metabolic processes of nitrogen-containing compounds. C-Nitroso compounds have a rich organic chemistry in their own right, displaying interesting intra- and intermolecular dimerization processes and addition reactions with unsaturated compounds. In addition, they have a fascinating coordination chemistry. While most of the attention has been directed towards C-nitroso compounds containing a single -NO moiety, there is an emerging area of research dealing with dinitroso and polynitroso compounds. In this critical review, we present and discuss the synthetic routes and properties of these relatively unexplored dinitroso and polynitroso compounds, and suggest areas of further development involving these compounds. (126 references.).     

Tandem reactions initiated by copper-catalyzed cross-coupling: a new strategy towards heterocycle synthesis

Copper-catalyzed cross-coupling reactions which lead to the formation of C-N, C-O, C-S and C-C bonds have been recognized as one of the most useful strategies in synthetic organic chemistry. During past decades, important breakthroughs in the study of Cu-catalyzed coupling processes demonstrated that Cu-catalyzed reactions are broadly applicable to a variety of research fields related to organic synthesis. Representatively, employing these coupling transformations as key steps, a large number of tandem reactions have been developed for the construction of various heterocyclic compounds. These tactics share the advantages of high atom economics of tandem reactions as well as the broad tolerance of Cu-catalyst systems. Therefore, Cu-catalyzed C-X (X = N, O, S, C) coupling transformation-initiated tandem reactions were quickly recognized as a strategy with great potential for synthesizing heterocyclic compounds and gained worldwide attention. In this review, recent research progress in heterocycle syntheses using tandem reactions initiated by copper-catalyzed coupling transformations, including C-N, C-O, C-S as well as C-C coupling processes are summarized.     

Ketenes in polymer-assisted synthesis

Since its inception, ketene chemistry has developed into a unique and well-established source of useful transformations for conventional synthetic organic chemistry. It is, therefore, not surprising that soon after their movement from the realm of peptide and peptoid libraries to that of small molecules, combinatorial chemists have sought the benefits of ketene chemistry to satisfy their own synthetic needs. The ability of these versatile molecules to undergo reactions with nucleophiles, and to participate in cycloadditions and cyclocondensations, has been utilized for the preparation of diverse heterocyclic compounds, and has added to the advantages of polymer-assisted synthesis for rapid purification. Different types of ketenes and different methods for their generation have been involved, which illustrates the potential diversity of the chemistry. There is now a better grasp of the effect of the fragility of these sometimes transient molecules on the reactions involving solid supports, and this augurs well for the application of some of the more recent developments in ketene chemistry to the generation of small-molecule libraries.     

Recent Advances in Organic Reactions Catalyzed by Lanthanide(III) Complexes

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Recent advances in the application of sulfinic acids for the construction of sulfur-containing compounds

Sulfur-containing organic compounds display wide applications in the field of materials science, synthetic chemistry, and pharmaceutical industry. Thus, numerous synthetic strategies have been developed for the synthesis of sulfur-containing compounds in synthetic chemistry. In recent years, the utilization of sulfinic acids as versatile synthons has emerged as attractive and powerful approach to access various organosulfur compounds through sulfonylation, sulfinylation or sulfenylation reaction...     

Asymmetric Catalytic Approaches Employing α,β-Unsaturated Imines

Nitrogen-containing heterocyclic compounds have consistently been a noticeable center of attention due to their significant utilization in the domain of synthetic organic chemistry, agrochemicals, and pharmaceuticals. α,β-Unsaturated imines or conjugated imines provide a lot of significant cyclic as well as acyclic products through reacting with a versatile family of compounds. This review summarizes the recent advances in enantioselective reactions of α,β-unsaturated imines by using synthetic methodologies for synthesizing various nitrogen-containing heterocycles that contain four to six-membered rings. The synthesis of rarely found seven-, eight- and nine-membered nitrogen-containing heterocycles have also been reported.     

钴萘酞菁的合成

采用Diels-Alder方法合成了2,3-萘二腈和6,7-二溴-2,3-萘二腈化合物,并以此为前体成功地合成了相应的钴萘酞菁系列化合物---一种新型的功能有机材料。另外还探讨了酞菁形成的机理,并讨论了若干影响因素。这些化合物具有较好的稳定性,在胺类或其它含氮的有机溶剂中有较好的溶解度,如苯胺、二甲基甲酰胺(DMF)或吡啶等。     

Isomerization of cyclobutane ligands in the solid state and solution

Cyclobutane compounds are a class of compounds that can be conveniently synthesized in the solid state by employing crystal engineering principles. The rctt-isomer (or the syn-dimer) is the most common form of any cyclobutene compound that is obtained in the solid state by the photochemical [2 + 2] cycloaddition reactions. However, these rctt-isomers can be converted to other less accessible forms, under some special conditions. Isomerization of cyclobutane compounds thus plays an important role in synthetic chemistry. Such isomerization of cyclobutane compounds have been reported in organic salts, metal complexes, coordination polymers and metal-organic frameworks. In this review, these fascinating examples of isomerization that occur both in the solid state and solution phase have been discussed.     

The synthesis of chromenes, chromanes, coumarins and related heterocycles via tandem reactions of salicylic aldehydes or salicylic imines with alpha,beta-unsaturated compounds

The tandem reactions of salicylic aldehydes or salicylic imines with alpha,beta-unsaturated compounds have only been studied systematically in recent years. These tandem reactions provide an easy access to a variety of heterocycles, such as chromanes, chromenes, coumarins and tetrahydroxanthenones, many of which are synthetic useful intermediates.