Examination of nature's favorite molecules reveals a striking preference for making carbon-heteroatom bonds over carbon-carbon bonds-surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon-heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C-C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C-X-C), an approach we call "click chemistry". Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect "spring-loaded" reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820010601%2940%3A11%3C2004%3A%3AAID-ANIE2004%3E3.0.CO%3B2-5

Click Chemistry: Diverse Chemical Function from a Few Good Reactions.

Direct C-H transformation via iron catalysis.

Starting from the early 1990’s, the chemistry of polyvalent iodine organic compounds has experienced an explosive development. This surging interest in iodine compounds is mainly due to the very useful oxidizing properties of polyvalent organic iodine reagents, combined with their benign environmental character and commercial availability. Iodine(III) and iodine(V) derivatives are now routinely used in organic synthesis as reagents for various selective oxidative transformations of complex organic molecules. Several areas of hypervalent organoiodine chemistry have recently attracted especially active interest and research activity. These areas, in particular, include the synthetic applications of 2-iodoxybenzoic acid (IBX) and similar oxidizing reagents based on the iodine(V) derivatives, the development and synthetic use of polymer-supported and recyclable polyvalent iodine reagents, the catalytic applications of organoiodine compounds, and structural studies of complexes and supramolecular assemblies of polyvalent iodine compounds.

The chemistry of polyvalent iodine has previously been covered in four books1–4 and several comprehensive review papers.5–17 Numerous reviews on specific classes of polyvalent iodine compounds and their synthetic applications have recently been published.18–61 Most notable are the specialized reviews on [hydroxy(tosyloxy)iodo]benzene,41 the chemistry and synthetic applications of iodonium salts,29,36,38,42,43,46,47,54,55 the chemistry of iodonium ylides,56–58 the chemistry of iminoiodanes,28 hypervalent iodine fluorides,27 electrophilic perfluoroalkylations,44 perfluoroorgano hypervalent iodine compounds,61 the chemistry of benziodoxoles,24,45 polymer-supported hypervalent iodine reagents,30 hypervalent iodine-mediated ring contraction reactions,21 application of hypervalent iodine in the synthesis of heterocycles,25,40 application of hypervalent iodine in the oxidation of phenolic compounds,32,34,50–53,60 oxidation of carbonyl compounds with organohypervalent iodine reagents,37 application of hypervalent iodine in (hetero)biaryl coupling reactions,31 phosphorolytic reactivity of o-iodosylcarboxylates,33 coordination of hypervalent iodine,19 transition metal catalyzed reactions of hypervalent iodine compounds,18 radical reactions of hypervalent iodine,35,39 stereoselective reactions of hypervalent iodine electrophiles,48 catalytic applications of organoiodine compounds,20,49 and synthetic applications of pentavalent iodine reagents.22,23,26,59

The main purpose of the present review is to summarize the data that appeared in the literature following publication of our previous reviews in 1996 and 2002. In addition, a brief introductory discussion of the most important earlier works is provided in each section. The review is organized according to the classes of organic polyvalent iodine compounds with emphasis on their synthetic application. Literature coverage is through July 2008.

Chemistry of Polyvalent Iodine

Catalytic transformation of ubiquitous C–H bonds into valuable C–N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C–H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications

5.7. [32π + 32σ] Cycloadditions 74 5.8. [44π + 22π] Cycloadditions 75 6. Seven-Membered Ring Formation 78 6.1. [44π + 32σ] Cycloadditions 78 6.2. [52π+2σ + 22π] Cycloadditions 79 7. Eight-Membered Ring Formation 79 7.1. [22π + 22π + 22π + 22π] Cycloadditions 80 7.2. [44π + 22π + 22π] Cycloadditions 80 7.3. [44π + 44π] Cycloadditions 81 7.4. [66π + 22π] Cycloadditions 83 8. Ten-Membered Ring Formation 85 9. Conclusion and Remarks 87

Transition Metal-Mediated Cycloaddition Reactions

N-Substituted aziridines are formed by Fe- or Mn-Porphyrin catalysed reactions of PhlNR compounds (R = tosyl or COCF7) with alkenes; the stereochemical characteristics of these reactions are very different from those of the analogous epoxidation of the alkenes by PhlO.

Iron- and manganese-porphyrin catalysed aziridination of alkenes by tosyl- and acyl-iminoiodobenzene

Allylic amination of alkenes by tosyliminoiodobenzene: manganese porphyrins as suitable catalysts

meso-Tetra-arylporphyriniron(III) derivatives catalyse the N-tosylaziridination of aryl-substituted styrenes by tosylimidoiodobenzene, PhlNTs, a nitrogen analogue of iodosylbenzene. Three secondary reactions were found to limit the yield of N-tosylaziridination: (i) the formation of toluene-p-sulphonamide, TsNH2, which is presumably derived from hydrolysis of a possible iron-nitrene, FeNTs, intermediate, (ii) the conversion of the Fe(TPP)(Cl)(TPP = tetraphenylporphyrin) catalyst into an iron(III) complex where the NTs moiety is inserted into an iron-nitrogen bond of Fe(TPP)(Cl), (iii) an oxidative degradation of the porphyrin catalyst. These secondary reactions were avoided to a great extent by using anhydrous conditions and Fe(TDCPP)(ClO4)(TDCPP = tetrakis-2,6-dichlorophenylporphyrin) as a catalyst instead of Fe(TPP)(Cl) and Fe(TPP)(ClO4). Under these conditions, N-tosylaziridination of styrene, cis- and trans-stilbene, and 1,1-diphenylethylene was performed with yields between 40 and 90%. Fe(TDCPP)(ClO4) was also found to be the best catalyst for N-tosylaziridination of aliphatic alkenes such as hex-1-ene, cyclo-octene, and cis-and trans-hex-2-enes. Although N-tosylaziridination of the two latter alkenes catalysed by Fe(TPP)(Cl) was not stereospecific, this reaction became stereospecific with Fe(TDCPP)(ClO4) as catalyst. These results show that by a proper choice of the porphyriniron catalyst, relatively good yields of N-tosylaziridination of alkenes by PhlNTs can be obtained. As for 1,2-disubstituted aliphatic alkenes, syn addition of the NTs moiety to the double bond takes place. A possible mechanism is presented.

Aziridination of alkenes catalysed by porphyrinirons: selection of catalysts for optimal efficiency and stereospecificity

Dans les conditions les plus anhydres possibles, les porphyrines de fer et de manganese catalysent la tosylamination des alcanes par le tosylimidoiodobenzene, Phl=NTs, analogue azote de l'iodosylbenzene. Le meilleur catalyseur employe, Mn(TDCPP=tetra-2,6-dichlorophenylporphyrine) (CF 3 SO 3 ), conduit a la tosylamination du cyclohexane, de l'heptane et de l'adamantane avec des rendements entre 13 et 56%

Amination of alkanes catalyzed by iron- and manganese-porphyrins: particular selectivity for ω and ω−1 oxidations of linear alkanes

Iron-porphyrin-nitrene complexes: preparation, properties, and crystal structure of porphyrin-iron(III) complexes with a tosylnitrene inserted into an iron-nitrogen bond

G. Bedi

Papers

Iron- and manganese-porphyrin catalysed aziridination of alkenes by tosyl- and acyl-iminoiodobenzene

Allylic amination of alkenes by tosyliminoiodobenzene: manganese porphyrins as suitable catalysts

Aziridination of alkenes catalysed by porphyrinirons: selection of catalysts for optimal efficiency and stereospecificity

Amination of alkanes catalyzed by iron- and manganese-porphyrins: particular selectivity for ω and ω−1 oxidations of linear alkanes

Iron-porphyrin-nitrene complexes: preparation, properties, and crystal structure of porphyrin-iron(III) complexes with a tosylnitrene inserted into an iron-nitrogen bond