58861-54-4Relevant articles and documents
Manganese-Mediated C–H Bond Activation of Fluorinated Aromatics and the ortho-Fluorine Effect: Kinetic Analysis by In Situ Infrared Spectroscopic Analysis and Time-Resolved Methods
Athavan, Gayathri,Bishop, Amy L.,Bray, Joshua T. W.,Burden, Thomas J.,Clark, Ian P.,Clarke, Francis,Eastwood, Jonathan B.,Fairlamb, Ian J. S.,Hammarback, L. Anders,Jordan, Christina,Krieger, Jean-Philippe,Lynam, Jason M.,Robinson, Alan,Towrie, Michael,Whitwood, Adrian
, p. 1532 - 1544 (2022/01/28)
Insights into the factors controlling the site selectivity of transition metal-catalyzed C–H bond functionalization reactions are vital to their successful implementation in the synthesis of complex target molecules. The introduction of fluorine atoms into substrates has the potential to deliver this selectivity. In this study, we employ spectroscopic and computational methods to demonstrate how the “ortho-fluorine effect” influences the kinetic and thermodynamic control of C–H bond activation in manganese(I)-mediated reactions. The C–H bond activation of fluorinated N,N-dimethylbenzylamines and fluorinated 2-phenylpyridines by benzyl manganese(I) pentacarbonyl BnMn(CO)5 leads to the formation of cyclomanganated tetracarbonyl complexes (2a–b and 4a–e), which all exhibit C–H bond activation ortho-to-fluorine. Corroboration of the experimental findings with density functional theory methods confirms that a kinetically controlled irreversible σ-complex-assisted metathesis mechanism is operative in these reactions. The addition of benzoic acid results in a mechanistic switch, so that cyclomanganation proceeds through a reversible AMLA-6 mechanism (kinetically and thermodynamically controlled). These stoichiometric findings are critical to catalysis, particularly subsequent insertion of a suitable acceptor substrate into the C–Mn bond of the regioisomeric cyclomanganated tetracarbonyl complex intermediates. The employment of time-resolved infrared spectroscopic analysis allowed for correlation of the rates of terminal acetylene insertion into the C–Mn bond with the relative thermodynamic stability of the regioisomeric complexes. Thus, more stable manganacycles, imparted by an ortho-fluorine substituent, exhibit a slower rate of terminal acetylene insertion, whereas a para-fluorine atom accelerates this step. A critical factor in governing C–H bond site selectivity under catalytic conditions is the generation of the regioisomeric cyclomanganated intermediates, rather than their subsequent reactivity toward alkyne insertion.
Transition-Metal-Free Decarboxylative Arylation of 2-Picolinic Acids with Arenes under Air Conditions
Zhang, Xitao,Feng, Xiujuan,Zhou, Chuancheng,Yu, Xiaoqiang,Yamamoto, Yoshinori,Bao, Ming
supporting information, p. 7095 - 7099 (2018/11/23)
A facile, transition-metal-free, and direct decarboxylative arylation of 2-picolinic acids with simple arenes is described. The oxidative decarboxylative arylation of 2-picolinic acids with arenes proceeds readily via N-chloro carbene intermediates to afford 2-arylpyridines in satisfactory to good yields under transition-metal-free conditions. This new type of decarboxylative arylation is operationally simple and scalable and exhibits high functional-group tolerance. Various synthetically useful functional groups, such as halogen atoms, methoxycarbonyl, and nitro, remain intact during the decarboxylative arylation of 2-picolinic acids.
Blue light mediated C-H arylation of heteroarenes using TiO2 as an immobilized photocatalyst in a continuous-flow microreactor
Fabry, David C.,Ho, Yee Ann,Zapf, Ralf,Tremel, Wolfgang,Panth?fer, Martin,Rueping, Magnus,Rehm, Thomas H.
supporting information, p. 1911 - 1918 (2017/06/09)
Titanium dioxide was applied as an immobilized photocatalyst in a microstructured falling film reactor for the continuous-flow C-H arylation of heteroarenes with aryldiazonium salts as the starting material. Detailed investigations of the catalyst and a successful long-term run proved its excellent usability for this process. Very good yields up to 99% were achieved with broad substrate scope and were compared with batch synthesis. The transfer to the continuous-flow mode revealed an impressive boost in reactor performance solely resulting from the improved irradiation and contact of the catalyst, substrate and light.
