Recent advances in iron catalyzed reactions in organic synthesis

RECENT ADVANCES IN IRON CATALYZED REACTIONS IN ORGANIC SYNTHESIS JOURNAL OF ONGOING CHEMICAL RESEARCH 2020 Volume: 5 Issue: 2 Pages: 42-43 Document ID: 2020JOCR46 DOI: J Ong Chem Res, 2020, 5(2): 42-43, Document ID: 2020JOCR46, doi: Review Recent Advances in Iron Catalyzed Reactions in Organic Synthesis Farman Ullah Khan*, Shahid Hameed For affiliations and correspondence, see the last page. Abstract The transition metal catalyzed reactions are widely developed in current years. Most of the transition metals are expensive and are not easily available like; Gold (Au), Iridium (Ir), Palladium (Pd), Platinum (Pt), Ruthenium (Ru), Rhodium (Rh) etc. Iron is one of the highly plentiful, cheap and easily available transition metals. It has been consistently used in organic synthesis nowadays. In this review we have described the role of iron in organic reactions like C-C, C-O, C-N, C-S and N-S bond forming reactions. This review highlights the advancements in iron based organocatalysis from 2005 to 2020. Keywords: Organic Synthesis, Catalysis, Green Chemistry, Heterocycles, Transition Metals, Bond Forming The transition metals catalyzed reactions are an extremely helpful tools in organic-synthetic chemistry. The transition-metal-mediated organic processes are involved in the formation of carbon-carbon bonds and carbon-heteroatoms bonds that has become fundamental in the synthetic organic chemistry in few decades. The new methods for synthesis, reagents and catalysts have been developed in recent years to support in the synthesis of different chemical structures. The catalysts which have more reactivity, or the higher efficiency are playing an active role in chemicals research [1]. For a particular application the catalyst and organometallic reagent is selected based on different factors. For example, the compatibility with different functional groups and protecting groups, thermal stability of the substrate, the desire for stereo and regiospecificity, economic factor and operation ease [2]. The transition metals (like Palladium) catalyzed reactions make more than 60% carbon bond formations which are used in medicinal-chemistry these days [3]. The residual contamination issue is raised due to the use of palladium. This can cause the subsequent transformations and even patients health can be affected [4]. Many reactions reported to date require the use of precious-metals like; Palladium (Pd), Rhodium (Rh), Platinum (Pt), Gold (Au), and Ruthenium (Ru). The inherent toxicity and environmental impact is caused by these catalysts [5]. Therefore, the development of more sustainable and environment friendly reactions catalyzed through more benign-metal are needed to be investigated [6]. Iron can be of the appealing alternate to palladium as it is low cost, broadly available and have low toxicity [7-8]. Significant advances are made in the fields of iron catalyzed reactions in the past few years especially, in the carbon-carbon bond making, carbonoxygens bond formation, carbon to nitrogens bond formation, nitrogen-sulfurs bond formations. These bond formation reactions have arisen as a powerful tool and various functionalized compounds like amino acids, ketones, carboxylic acids, and so on has been prepared [9-11]. Here we have described different iron catalyzed organic reactions which are divided into four parts. The part 1 includes the carbon carbon bonds formation reactions. In the second part of This review we have discussed Iron catalyzed carbon oxygen bond formations reaction. In the third part of this review, we have discussed the carbon nitrogen bond formation reactions which are catalyzed with iron. Here 2 articles are discussed. At last we have also discussed ironcatalyzed N-S bond formation. 1. C-C bond formation 1.1 Carbon−carbon oxidative homo-coupling of alkenyl-lithiums: The coupling reaction of grignard reagents oxidatively catalyzed through iron-based transition metals have been actively investigated recently. Since 1969, the stoichiometric amount of FeCl3 for oxidative homocoupling of vinyllithium are reported. Z. Zhong et al. (2019), reported an effective iron catalyzed oxidative Farman Ullah Khan 42/52 J Ong Chem Res, 2020, 5(2): 42-43, Document ID: 2020JOCR46, doi: Review homocoupling of alkenyl lithiums. These were produced via lithium−halide direct exchange or by acetylenic lithium reagent cyclization. Which were covering different 1,3-butadiene like, polycyclic or acyclic multi-substituted 1,3-butadienes. At the start they used stoichiometric amount of FeCl3 and obtained the desired product of 1,3-buadiene in 86 % yield. They reported that by decreasing loading of FeCl3 and absence of oxidant lead to lower yield. The DTBP (ditert-butyl peroxide) was used as an oxidant which gave 86% yields. The solvent and temperatures were observed to have no role in yields improvement. They also observed that homocoupling of aryl groups with electron deficient substituents were slightly disrelished and lead to 49 to 58 % yield. Electron donating groups on aromatic rings increased the yield. Even the diene of natural product dimer was obtained in 47-77% yield. They observed that the tandem cyclization/oxidative coupling for acetylenic phenyl iodides led to higher yields than acetylenic alkyl iodides. Their work is shown in the figure 1 [12]. ransfer methodology which provide carbonyl compounds with β-branch in very good yield. The aliphatic alcohols and aromatic alcohols both can be used. The results from labelling study show that the source of hydride is secondary alcohol, while the alkylation in cobalt presence, no reversible step occur in this process. As a result, the alkylation will be diastereoselective. This work is shown in figure 2 [13]. Figure 2. Iron-catalyzed with secondary alcohols α-alkylation of ketones 1.3 Iron-catalyzed β‑ alkylation of alcohols: Bettoni et al. (2019), prepared β-Branched alkylated alcohols with diaminocyclopentadienone iron tricarbonyl-complex Fe1. They performed alkylations of 2-arylethanol derivatives. Benzylic alcohols and methanol were used for alkylation under milder condition. They used iron catalyzed methylation’ and benzylations of 2-arylethanol which gave β-methylated or β-benzylated alcohols in considerble yield. Figure 1. Oxidative homo-coupling of alkenyllithiums 1.2 Iron catalyzed α-alkylation of ketones with secondary alcohols: Bettoni et al. (2020) reported the alkylation of sterically hinderd aromatic ketone with different secondary alcohol’s by iron complex catalyzed phosphine free complex. They used hydrogen’s autot- Figure 3. Iron catalyzed double hydrogen autotransfer alkylation Different functionalities, like heterocyclic fragment, Farman Ullah Khan 43/52 J Ong Chem Res, 2020, 5(2): 42-43, Document ID: 2020JOCR46, doi: Review can be inserted on the aryl rings. These results confirm the synthesis of functionalize alcohol. This pathway can be alternatively used for hydroformylation and hydrogenatio (...truncated)