Cascade reactions iron-catalyzed

CuFc204 nanoparticles are an efficient catalyst for the synthesis of 4-methylcoumarins via Pechmann reaction of phenols with ethyl acetoac-etate in water at room temperature (14SC697). A similar Pechmann reaction of phenols with ethyl 4,4,4-trifluoroacetoacetate catalyzed by molecular iodine affords 4-trifluoromethylcoumarins (14TL6715). Highly functionalized coumarins are formed by an iron(III) chloride-mediated cascade reaction of salicylaldehydes or 2 -hydroxyacetophenones with various activated methylene compounds (14SC1507). 

Miscellaneous Gold- and Iron-Catalyzed Cascade Reactions The car-benic reactivity of gold catalysis was exploited toward the synthesis of stereoselective six-membered ring carbocycles, through cyclopropanation reactions incorporated in cascade sequences [31]. 

Iron-Catalyzed CDC Reactions as a Tool to Generate Molecular Complexity Cascade Reactions... 

CASCADE REACTIONS CATALYZED BY RUTHENIUM, IRON, IRIDIUM, RHODIUM, AND COPPER... 

Significant progress has been made in the fields of ruthenium-, iron-, iridium-, rhodium-, and copper-catalyzed cascade reactions. Noticeably, these transition metal catalysts are critically important in numerous commercial chemical processes. Discoveries of new cascade processes along with improvements in the activity, selectivity, and scope of these catalysts could drastically reduce the environmental impact and increase the sustainability of chemical reactions. From the viewpoint of practical applications, iron and copper are the most abundant metals on Earth and, consequently, inexpensive and environmentally friendly. Moreover, many iron and copper salts and complexes are commercially available or are described in the literature. Due to these advantages, the development and applications of iron- and copper-catalyzed cascade reactions are becoming a thriving area of organic synthesis chemistry. 

At nearly the same time MacMillan and coworkers developed a new protocol for SOMO-catalyzed intramolecular arylation of enolizable aldehydes (Scheme 4.7) [33]. In these studies the required oxidation step was accomplished by tris-phenanthroline complexes of iron]111) bearing non-nucleophilic counterions, such as Fe(phen)3-(PFd3. Higher degrees of enanhoselectivities were obtained compared to oxidations with CAN (see 34, Scheme 4.7). Using this method a simple three-step-access to (-)-tashiromine was elaborated by the authors. For theorehcal calculahons of this transformation see Reference [34], By extension of this concept to suitable requisite tethered polyenes the authors were able to estab-hsh a powerfijl cascade reaction leading to defined configured polycyclic structures (36, Scheme 4.7). The oxidation step in this process was achieved by slow addition of Cu(OTf)2/TFA sodium salt [35]. 

Electron-transfer (ET) reactions play a central role in all biological systems ranging from energy conversion processes (e.g., photosynthesis and respiration) to the wide diversity of chemical transformations catalyzed by different enzymes (1). In the former, cascades of electron transport take place in the cells where multicentered macromolecules are found, often residing in membranes. The active centers of these proteins often contain transition metal ions [e.g., iron, molybdenum, manganese, and copper ions] or cofactors as nicotinamide adenine dinucleotide (NAD) and flavins. The question of evolutionary selection of specific structural elements in proteins performing ET processes is still a topic of considerable interest and discussion. Moreover, one key question is whether such stmctural elements are simply of physical nature (e.g., separation distance between redox partners) or of chemical nature (i.e., providing ET pathways that may enhance or reduce reaction rates). 

In this chapter we described [2 + 2 + 2] and related cycloaddition reactions using palladium, iron, manganese, rhenium, and other transition metals. Palladium complexes are able to catalyze [2 + 2 + 2] and related cycloaddition reactions, which proceed via cascade-type mechanism or metallacycle intermediates. It is worthy of note that arynes are suitable substrates for this palladium catalysis. Iron complexes are promising catalysts for practical [2 + 2 + 2] cycloaddition reactions, owing to their low cost and nontoxicity, although both catalytic activity and substrate scope are not satisfactory. Manganese and rhenium complexes allow the use of 3-keto esters as a cycloaddition partner. To realize the practical process and broaden the product scope, further development of new transition-metal catalysts is expected in this research field. 

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