Iron Catalysis in Organic Synthesis

Transition metal-catalyzed direct functionalization of C–H bonds is one of the key emerging strategies that is currently attracting tremendous attention with the aim to provide alternative environmentally friendly and efficient ways for the construction of C–C and C–hetero bonds. In particular, the strategy involving regioselective C–H activation assisted by various functional groups shows high potential, and significant achievements have been made in both the development of novel reactions and the mechanistic study. In this review, we attempt to give an overview of the development of utilizing the functionalities as directing groups. The discussion is directed towards the use of different functional groups as directing groups for the construction of C–C and C–hetero bonds via C–H activation using various transition metal catalysts. The synthetic applications and mechanistic features of these transformations will be discussed, and the review is organized on the basis of the type of directing groups and the type of bond being formed or the catalyst.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

Copper-catalyzed C-H functionalization reactions: efficient synthesis of heterocycles.

Synthesis of heterocycles via electrophilic cyclization of alkynes containing heteroatom.

The advance in the area of synthesis and reactivity of organoselenium, as well as the discovery that selenium was the cause of severe intoxication episodes of livestock in the 1930s and the subsequent determination that selenium was an essential trace element in the diet for mammals, has motivated intense studies of the biological properties of both organic and inorganic selenium compounds. In this review, we shall cover a wide range of toxicological and pharmacological effects, in which organoselenium compounds are involved but the effects of inorganic compounds were not discussed in detail here. The molecular toxicity of inorganic selenium was described in relation to its interaction with endogenous –SH groups to allow a comparison with that of synthetic organoselenium compounds. Furthermore, in view of the recent points of epidemiological evidence that overexposure to selenium can facilitate the appearance of chronic degenerative diseases, we also briefly revised the history of selenium toxicity and physiology and how environmental selenium can reach inside the mammalian cells. The biological narrative of the element selenium, in the last century, has been marked by a contrast between its toxic and its beneficial effects. Thus, the potential therapeutic use of simple organoselenium compounds has not yet been sufficiently explored and, consequently, we cannot discard this class of compounds as promising pharmaceutical agents. In effect, the future of the organochalcogens as pharmacological agents will depend on more detailed toxicological studies in the oncoming years.

Toxicology and pharmacology of selenium: emphasis on synthetic organoselenium compounds

Oral administration of diphenyl diselenide protects against cadmium-induced liver damage in rats.

A series of 4-Se-(Te, S)-isochromenones and 3-substituted isochromenones were synthesized in good yields via FeCl3-mediated cyclization of alkynylaryl esters with different diorganyl dichalcogenides This methodology was carried out at room temperature, using inexpensive and environmentally friendly iron salts as metallic source and under air atmosphere The reaction showed to be tolerant to a range of substituents bonded into the aromatic ring of the diorganyl dichalcogenides as well as to alkyl groups directly bonded to the chalcogen atom Alternatively, the cyclization reaction of 2-alkynylaryl esters with FeCl3, in the absence of diorganyl dichalcogenide, gave the isochromenones without the chalcogen moiety in the structure This approach proved to be highly regioselective, providing only six-membered ring products, once the possible five-membered products were not observed in any experiments

Regioselective synthesis of isochromenones by iron(III)/PhSeSePh-mediated cyclization of 2-alkynylaryl esters.

We herein described the synthesis of various organochalcogen propargyl aryl ethers via reaction of lithium acetylide intermediate with electrophilic chalcogen (sulfur, selenium, tellurium) species....

Synthesis of organochalcogen propargyl aryl ethers and their application in the electrophilic cyclization reaction: an efficient preparation of 3-halo-4-chalcogen-2H-benzopyrans.

This report describes the synthesis of 4-organoselenylisoxazoles via FeCl3/RSeSeR-mediated intramolecular cyclization of alkynone O-methyloximes. The optimized conditions allowed the cyclization to proceed at room temperature under ambient atmosphere, and the reaction requires a short time to be completed. The reaction conditions tolerated neutral, electron-donating and electron-withdrawing groups present in both substrates, alkynone O-methyloximes and diorganyl diselenides. Treatment of 4-organoselenylisoxazoles with n-butyllithium, followed by trapping with electrophiles, furnished the functionalized isoxazoles in good yields. The obtained products also proved to be suitable substrates for the preparation of 4-bromoisoxazoles via Br/Se exchange reaction.

Benhur Godoi

Papers

Synthesis of heterocycles via electrophilic cyclization of alkynes containing heteroatom.

Oral administration of diphenyl diselenide protects against cadmium-induced liver damage in rats.

Regioselective synthesis of isochromenones by iron(III)/PhSeSePh-mediated cyclization of 2-alkynylaryl esters.

Synthesis of organochalcogen propargyl aryl ethers and their application in the electrophilic cyclization reaction: an efficient preparation of 3-halo-4-chalcogen-2H-benzopyrans.

Iron(III) chloride/diorganyl diselenides: a tool for intramolecular cyclization of alkynone O-methyloximes.