18228-44-9Relevant articles and documents
The chromium(II)-mediated coupling of secondary alkylhalides with aromatic aldehydes
Wessjohann, Ludger A.,Schmidt, Gisela,Schrekker, Henri S.
, p. 2139 - 2141 (2007)
The scope of chromium(II)-mediated Takai-Utimoto reactions was extended to previously unconvertable secondary alkylhalides. Optimization allowed yields of up to over 95%. Georg Thieme Verlag Stuttgart.
Carbon monoxide and hydrogen (syngas) as a C1-building block for selective catalytic methylation
Kaithal, Akash,H?lscher, Markus,Leitner, Walter
, p. 976 - 982 (2021/02/06)
A catalytic reaction using syngas (CO/H2) as feedstock for the selective β-methylation of alcohols was developed whereby carbon monoxide acts as a C1 source and hydrogen gas as a reducing agent. The overall transformation occurs through an intricate network of metal-catalyzed and base-mediated reactions. The molecular complex [Mn(CO)2Br[HN(C2H4PiPr2)2]]1comprising earth-abundant manganese acts as the metal component in the catalytic system enabling the generation of formaldehyde from syngas in a synthetically useful reaction. This new syngas conversion opens pathways to install methyl branches at sp3carbon centers utilizing renewable feedstocks and energy for the synthesis of biologically active compounds, fine chemicals, and advanced biofuels.
Highly efficient NHC-iridium-catalyzed β-methylation of alcohols with methanol at low catalyst loadings
Lu, Zeye,Zheng, Qingshu,Zeng, Guangkuo,Kuang, Yunyan,Clark, James H.,Tu, Tao
, p. 1361 - 1366 (2021/06/30)
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.].
Manganese(I)-Catalyzed β-Methylation of Alcohols Using Methanol as C1 Source
Kaithal, Akash,van Bonn, Pit,H?lscher, Markus,Leitner, Walter
supporting information, p. 215 - 220 (2019/12/03)
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.
Ruthenium(II)-Catalyzed β-Methylation of Alcohols using Methanol as C1 Source
Kaithal, Akash,Schmitz, Marc,H?lscher, Markus,Leitner, Walter
, p. 5287 - 5291 (2019/05/28)
Selective introduction of methyl branches into the carbon chains of alcohols can be achieved with low loadings of ruthenium precatalyst [RuH(CO)(BH4)(HN(C2H4PPh2)2)] (Ru-MACHO-BH) using methanol both as methylating reagent and as reaction medium. A wide range of structurally divers alcohols was β-methylated with excellent selectivity (>99 %) in fair to high yields (up to 94 %) under standard conditions, and turnover numbers up to 18,000 could be established. The overall reaction rate of the complex catalytic network appears to be governed by interconnection of the individual subcycles through availability of the reactive intermediates. The synthetic procedure opens pathways to important structural motifs following the Green Chemistry principles.
Synthesis of Halomethyl Isoxazoles/Cyclic Nitrones via Cascade Sequence: 1,2-Halogen Radical Shift as a Key Link
Chen, Hong-Lei,Wei, Dian,Zhang, Jian-Wu,Li, Cheng-Lin,Yu, Wei,Han, Bing
supporting information, p. 2906 - 2910 (2018/05/28)
A novel iminoxyl radical-promoted dichotomous regioselective 5-exo-trig cyclization onto vinylic halogen/1,2-halogen radical shift sequence is developed for the synthesis of halomethyl isoxazoles/cyclic nitrones using β-halo-β,?- and ?-halo-?,?-unsaturated ketoximes as the substrates and PhI(OAc)2/TEMPO as the oxidation system. DFT calculations reveal that a halogen-bridged three-membered ring transition state is involved in the 1,2-Cl-/Br-atom shift, while the 1,2-I atom migration can be taken into account with an elimination/readdition mechanism. The migration ability was indicated to be ranked in the following order: I > Br > Cl.
C -Methylation of Alcohols, Ketones, and Indoles with Methanol Using Heterogeneous Platinum Catalysts
Siddiki, S. M. A. Hakim,Touchy, Abeda S.,Jamil, Md. A. R.,Toyao, Takashi,Shimizu, Ken-Ichi
, p. 3091 - 3103 (2018/04/14)
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.
Iridium Clusters Encapsulated in Carbon Nanospheres as Nanocatalysts for Methylation of (Bio)Alcohols
Liu, Qiang,Xu, Guoqiang,Wang, Zhendong,Liu, Xiaoran,Wang, Xicheng,Dong, Linlin,Mu, Xindong,Liu, Huizhou
, p. 4748 - 4755 (2017/12/15)
C?H methylation is an attractive chemical transformation for C?C bonds construction in organic chemistry, yet efficient methylation of readily available (bio)alcohols in water using methanol as sustainable C1 feedstock is limited. Herein, iridium nanocatalysts encapsulated in yolk–shell-structured mesoporous carbon nanospheres (Ir@YSMCNs) were synthesized for this transformation. Monodispersed Ir clusters (ca. 1.0 nm) were encapsulated in situ and spatially isolated within YSMCNs by a silica-assisted sol–gel emulsion strategy. A selection of (bio)alcohols (19 examples) was selectively methylated in aqueous phase with good-to-high yields over the developed Ir@YSMCNs. The improved catalytic efficiencies in terms of activity and selectivity together with the good stability and recyclability were contributable to the ultrasmall Ir clusters with oxidation chemical state as a consequence of the confinement effect of YSMCNs with interconnected nanostructures.
Preparation and use of DMF-stabilized iridium nanoclusters as methylation catalysts using methanol as the C1 source
Oikawa, Kei,Itoh, Satoshi,Yano, Hiroki,Kawasaki, Hideya,Obora, Yasushi
, p. 1080 - 1083 (2017/02/05)
We report methylations of alcohols and anilines catalyzed by DMF-stabilized Ir nanoclusters using methanol as the C1 source. The DMF-stabilized Ir nanoclusters were prepared in one step and have diameters of 1-1.5 nm. They react in a borrowing-hydrogen reaction and are efficient methylation catalysts (TON up to 310?000).
Halogen-bonded iodonium ion catalysis: A route to α-hydroxy ketones: Via domino oxidations of secondary alcohols and aliphatic C-H bonds with high selectivity and control
Guha, Somraj,Kazi, Imran,Mukherjee, Pranamita,Sekar, Govindasamy
supporting information, p. 10942 - 10945 (2017/10/13)
A domino synthesis of α-hydroxy ketones has been developed from benzylic secondary alcohols employing catalytic iodonium ions stabilized by DMSO. The reaction proceeds through an unprecedented sequential oxidation of alcohols to ketone and its α-hydroxylation in a controlled manner. The spectroscopic evidence establishes the possibility of formation of a stable halogen-bonded adduct between DMSO and iodonium ions.
