- Manganese(I)-Catalyzed β-Methylation of Alcohols Using Methanol as C1 Source
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Highly selective β-methylation of alcohols was achieved using an earth-abundant first row transition metal in the air stable molecular manganese complex [Mn(CO)2Br[HN(C2H4PiPr2)2]] 1 ([HN(C2H4PiPr2)2]=MACHO-iPr). The reaction requires only low loadings of 1 (0.5 mol %), methanolate as base and MeOH as methylation reagent as well as solvent. Various alcohols were β-methylated with very good selectivity (>99 %) and excellent yield (up to 94 %). Biomass derived aliphatic alcohols and diols were also selectively methylated on the β-position, opening a pathway to “biohybrid” molecules constructed entirely from non-fossil carbon. Mechanistic studies indicate that the reaction proceeds through a borrowing hydrogen pathway involving metal–ligand cooperation at the Mn-pincer complex. This transformation provides a convenient, economical, and environmentally benign pathway for the selective C?C bond formation with potential applications for the preparation of advanced biofuels, fine chemicals, and biologically active molecules.
- Kaithal, Akash,van Bonn, Pit,H?lscher, Markus,Leitner, Walter
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- Highly efficient NHC-iridium-catalyzed β-methylation of alcohols with methanol at low catalyst loadings
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The methylation of alcohols is of great importance since a broad number of bioactive and pharmaceutical alcohols contain methyl groups. Here, a highly efficient β-methylation of primary and secondary alcohols with methanol has been achieved by using bis-N-heterocyclic carbene iridium (bis-NHC-Ir) complexes. Broad substrate scope and up to quantitative yields were achieved at low catalyst loadings with only hydrogen and water as by-products. The protocol was readily extended to the β-alkylation of alcohols with several primary alcohols. Control experiments, along with DFT calculations and crystallographic studies, revealed that the ligand effect is critical to their excellent catalytic performance, shedding light on more challenging Guerbet reactions with simple alcohols. [Figure not available: see fulltext.].
- Lu, Zeye,Zheng, Qingshu,Zeng, Guangkuo,Kuang, Yunyan,Clark, James H.,Tu, Tao
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p. 1361 - 1366
(2021/06/30)
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- Iron-Catalyzed β-Alkylation of Alcohols
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β-Branched alkylated alcohols have been prepared in good yields using a double-hydrogen autotransfer strategy in the presence of our diaminocyclopentadienone iron tricarbonyl complex Fe1. The alkylation of some 2-arylethanol derivatives was successfully addressed with benzylic alcohols and methanol as alkylating reagents under mild conditions. Deuterium labeling experiments suggested that both alcohols (2-arylethanol and either methanol or benzyl alcohol) served as hydrogen donors in this cascade process.
- Bettoni, Leó,Gaillard, Sylvain,Renaud, Jean-Luc
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p. 8404 - 8408
(2019/10/16)
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- Iron-Catalyzed Borrowing Hydrogen β- C(sp3)-Methylation of Alcohols
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Herein we report the iron-catalyzed β-C(sp3)-methylation of primary alcohols using methanol as a C1 building block. This borrowing hydrogen approach employs a well-defined bench-stable (cyclopentadienone)iron(0) carbonyl complex as precatalyst (5 mol %) and enables a diverse selection of substituted 2-arylethanols to undergo β-C(sp3)-methylation in good isolated yields (24 examples, 65% average yield).
- Polidano, Kurt,Williams, Jonathan M. J.,Morrill, Louis C.
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p. 8575 - 8580
(2019/09/12)
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- C -Methylation of Alcohols, Ketones, and Indoles with Methanol Using Heterogeneous Platinum Catalysts
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A versatile, selective, and recyclable heterogeneous catalytic method for the methylation of C-H bonds in alcohols, ketones, and indoles with methanol under oxidant-free conditions using a Pt-loaded carbon (Pt/C) catalyst in the presence of NaOH is reported. This catalytic system is effective for various methylation reactions: (1) the β-methylation of primary alcohols, including aryl, aliphatic, and heterocyclic alcohols, (2) the α-methylation of ketones, and (3) the selective C3-methylation of indoles. The reactions are driven by a borrowing-hydrogen mechanism. The reaction begins with the dehydrogenation of the alcohol(s) to afford aldehydes, which subsequently undergo a condensation reaction with the nucleophile (aldehyde, ketone, or indole), followed by hydrogenation of the condensation product by Pt-H species to yield the desired product. In all of the methylation reactions explored in this study, the Pt/C catalyst exhibits a significantly higher turnover number than other previously reported homogeneous catalytic systems. Moreover, it is demonstrated that the high catalytic activity of Pt can be rationalized in terms of the adsorption energy of hydrogen on the metal surface, as revealed by density functional theory calculations on different metal surfaces.
- Siddiki, S. M. A. Hakim,Touchy, Abeda S.,Jamil, Md. A. R.,Toyao, Takashi,Shimizu, Ken-Ichi
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p. 3091 - 3103
(2018/04/14)
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- Catalytic enantioselective C-H functionalization of indoles with α-diazopropionates using chiral dirhodium(II) carboxylates: Asymmetric synthesis of the (+)-α-methyl-3-indolylacetic acid fragment of acremoauxin A
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An enantioselective C-H functionalization of N-methoxymethyl (MOM)-protected 2,3-unsubstituted indoles with α-diazopropionates has been effected via catalysis by dirhodium(II) tetrakis[N-phthaloyl-(S)- triethylalaninate], Rh2((S)-PTTEA)4, providing α-methyl-3-indolylacetates in high yields and with enantioselectivities of up to 86% ee. The effectiveness of this protocol was demonstrated by the first catalytic asymmetric synthesis of the (+)-α-methyl-3-indolylacetic acid fragment of acremoauxin A, a potent plant-growth inhibitor. Furthermore, the Fujioka protocol using a combination of TMSOTf and 2,2′-bipyridyl was shown to be superior for the removal of the N-MOM group.
- Goto, Takayuki,Natori, Yoshihiro,Takeda, Koji,Nambu, Hisanori,Hashimoto, Shunichi
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p. 907 - 915
(2011/08/09)
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- Tandem hydroformylation/Fischer indole synthesis: A novel and convenient approach to indoles from olefins
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(Matrix presented) A novel one-pot synthesis of indole systems via tandem hydroformylation/Fischer indole synthesis starting from olefins and arylhydrazines is described. This tandem procedure leads directly to 3-substituted indoles if unsubstituted phenylhydrazine is used and to 3,5- respectively 3,7-disubstituted indoles if para- or ortho-substituted arylhydrazines are used.
- Koehling, Petra,Schmidt, Axel M.,Eilbracht, Peter
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p. 3213 - 3216
(2007/10/03)
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- InBr3-catalyzed Friedel-Crafts addition of indoles to chiral aromatic epoxides: A facile route to enantiopure indolyl derivatives
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Aromatic optically active epoxides can be opened in a regioselective and clean way with indoles in the presence of catalytic amount of InBr3 (1 mol %). The reaction takes place with a SN2 pathway affording the 2-aryl-2-(3′-indolyl)-ethan-l-ols with excellent enantioselectivity (ee up to 99%).
- Bandini, Marco,Cozzi, Pier Giorgio,Melchiorre, Paolo,Umani-Ronchi, Achille
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p. 5386 - 5389
(2007/10/03)
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- Synthesis of Acremoauxin A, a New Plant Growth Regulator Produced by Acremonium roseum I 4267
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Acremoauxin A, a new fungal auxin derivative produced by A. roseum I 4267, was synthesized from indole, lactic acid, and D-mannitol. (+)-2-(3-Indolyl)propionic acid was prepared from its synthetic racemate by biological resolution using the acremoauxin-producing fungus.The synthetically confirmed structure of acremoauxin A was 1-O--D-arabitol (1).
- Yoshida, Noriyuki,Sassa, Takeshi
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p. 2681 - 2683
(2007/10/02)
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