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- Item3,3-Difluoroallyl ammonium salts: highly versatile, stable and selective gem-difluoroallylation reagents([London] : Nature Publishing Group UK, 2021) Ye, Fei; Ge, Yao; Spannenberg, Anke; Neumann, Helfried; Xu, Li-Wen; Beller, MatthiasThe selective synthesis of fluorinated organic molecules continues to be of major importance for the development of bioactive compounds (agrochemicals and pharmaceuticals) as well as unique materials. Among the established synthetic toolbox for incorporation of fluorine-containing units, efficient and general reagents for introducing -CF2- groups have been largely neglected. Here, we present the synthesis of 3,3-difluoropropen-1-yl ammonium salts (DFPAs) as stable, and scalable gem-difluoromethylation reagents, which allow for the direct reaction with a wide range of fascinating nucleophiles. DFPAs smoothly react with N-, O-, S-, Se-, and C-nucleophiles under mild conditions without necessity of metal catalysts with exclusive regioselectivity. In this way, the presented reagents also permit the straightforward preparation of many analogues of existing pharmaceuticals.
- ItemEfficient palladium-catalyzed synthesis of 2-aryl propionic acids(Basel : MDPI, 2020) Neumann, Helfried; Sergeev, Alexey G.; Spannenberg, Anke; Beller, MatthiasA flexible two-step, one-pot procedure was developed to synthesize 2-aryl propionic acids including the anti-inflammatory drugs naproxen and flurbiprofen. Optimal results were obtained in the presence of the novel ligand neoisopinocampheyldiphenylphosphine (NISPCPP) (9) which enabled the efficient sequential palladium-catalyzed Heck coupling of aryl bromides with ethylene and hydroxycarbonylation of the resulting styrenes to 2-aryl propionic acids. This cascade transformation leads with high regioselectivity to the desired products in good yields and avoids the need for additional purification steps. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemLigand-Controlled Palladium-Catalyzed Carbonylation of Alkynols : Highly Selective Synthesis of α-Methylene-β-Lactones(Weinheim : Wiley-VCH, 2020) Ge, Yao; Ye, Fei; Liu, Jiawang; Yang, Ji; Spannenberg, Anke; Jiao, Haijun; Jackstell, Ralf; Beller, MatthiasThe first general and regioselective Pd-catalyzed cyclocarbonylation to give α-methylene-β-lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N-arylated imidazole (L11) in the presence of Pd(MeCN)2Cl2 as pre-catalyst. A variety of easily available alkynols provide under additive-free conditions the corresponding α-methylene-β-lactones in moderate to good yields with excellent regio- and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemThe role of allyl ammonium salts in palladium-catalyzed cascade reactions towards the synthesis of spiro-fused heterocycles([London] : Nature Publishing Group UK, 2020) Ye, Fei; Ge, Yao; Spannenberg, Anke; Neumann, Helfried; Beller, MatthiasThere is a continuous need for designing new and improved synthetic methods aiming at minimizing reaction steps while increasing molecular complexity. In this respect, catalytic, one-pot cascade methodologies constitute an ideal tool for the construction of complex molecules with high chemo-, regio-, and stereoselectivity. Herein, we describe two general and efficient cascade procedures for the synthesis of spiro-fused heterocylces. This transformation combines selective nucleophilic substitution (SN2′), palladium-catalyzed Heck and C–H activation reactions in a cascade manner. The use of allylic ammonium salts and specific Pd catalysts are key to the success of the transformations. The synthetic utility of these methodologies is showcased by the preparation of 48 spiro-fused dihydrobenzofuranes and indolines including a variety of fluorinated derivatives.
- ItemEfficient methylation of anilines with methanol catalysed by cyclometalated ruthenium complexes(London : RSC Publ., 2021) Piehl, Patrick; Amuso, Roberta; Spannenberg, Anke; Gabriele, Bartolo; Neumann, Helfried; Beller, MatthiasCyclometalated ruthenium complexes4-10allow the effective methylation of anilines with methanol to selectively giveN-methylanilines. This hydrogen autotransfer procedure proceeds under mild conditions (60 °C) in a practical manner (NaOH as base). Mechanistic investigations suggest an active homogenous ruthenium complex and β-hydride elimination of methanol as the rate determining step. © The Royal Society of Chemistry 2021.
- ItemSynthesis of Molybdenum Pincer Complexes and Their Application in the Catalytic Hydrogenation of Nitriles(Weinheim : Wiley-VCH Verlag, 2020) Leischner, Thomas; Spannenberg, Anke; Junge, Kathrin; Beller, MatthiasA series of molybdenum(0), (I) and (II) complexes ligated by different PNP and NNN pincer ligands were synthesized and structurally characterized. Along with previously described Mo−PNP complexes Mo-1 and Mo-2, all prepared compounds were tested in the catalytic hydrogenation of aromatic nitriles to primary amines. Among the applied catalysts, Mo-1 is particularly well suited for the hydrogenation of electron-rich benzonitriles. Additionally, two aliphatic nitriles were transformed into the desired products in 80 and 86 %, respectively. Moreover, catalytic intermediate Mo-1a was isolated and its role in the catalytic cycle was subsequently demonstrated. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemPalladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds(Weinheim : Wiley-VCH, 2021) Ge, Yao; Ye, Fei; Yang, Ji; Spannenberg, Anke; Jiao, Haijun; Jackstell, Ralf; Beller, MatthiasA direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon–carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH