Top Event für europäische Jungchemiker

Transition‐Metal‐Free Alkoxycarbonylation of Aryl Halides

“…[3][4][5][6][7] Besides, transition metals, especially palladium-and manganese-catalyzed radical alkoxycarbonylation of alkyl iodides under photoirradiation conditions have also been developed to be an efficient approach towards the synthesis of carboxylic acid esters. [8][9][10][11][12][13] However, there are still some challenges such as the turnover numbers and turnover frequencies, which hinder its wide industrial application. Generally, low-valent-metal catalysts such as palladium(0) are required to activate the CÀX bond, whereas the strong binding ability of CO towards low-valent metals deactivate the catalyst, which present a challenge in this transformation.…”

Oxidative Catalysis Using the Stoichiometric Oxidant as a Reagent: An Efficient Strategy for Single‐Electron‐Transfer‐Induced Tandem Anion–Radical Reactions

“…SET-mediated reactions can be classified according to the overall change of the oxidation state as redox-neutral, oxidative, or reductive. Redox-neutral processes are often transition-metal-catalyzed cross-coupling reactions involving alkyl halides or sulfur electrophiles, [1,2] transition-metal-catalyzed atom-transfer radical reactions, [1,3] the more recently rediscovered homolytic aromatic substitutions, [1,4] tetrathiafulvalene-promoted radical reactions [5a] and cycloaddition reactions, [1] in which the catalytic SET oxidant or reductant is regenerated at the end of the catalytic cycle by the reverse electron transfer. The majority of the known SETinduced reactions are, however, overall reductive [1,5] or oxidative, [1,6] which means that at least two equal SET steps occur sequentially in the process.…”

“…They require stoichiometric amounts of SET oxidants or reducing agents to proceed. Catalytic versions are rare; notable are reductive titanium-(III)-catalyzed reactions, [1,7] photoredox-catalytic transformations, [1,8] and some Minisci-type reactions. [1] However, even though they are catalytic in the SET-active species, they always require sacrificial reductants or oxidants to achieve turnover, such as metals, tBuOOH, and amines, which end as waste after completion of the reaction (Figure 1).…”

“…Catalytic versions are rare; notable are reductive titanium-(III)-catalyzed reactions, [1,7] photoredox-catalytic transformations, [1,8] and some Minisci-type reactions. [1] However, even though they are catalytic in the SET-active species, they always require sacrificial reductants or oxidants to achieve turnover, such as metals, tBuOOH, and amines, which end as waste after completion of the reaction (Figure 1). [9] We hypothesized that it would be more environmentally sustainable to use the sacrificial reduced or oxidized species resulting from promotion of the SET steps productively to introduce useful functionality into the target molecules.…”

“…[11] Therefore the opposite process should proceed spontaneously and allow the catalytic SET oxidation. Indeed, an instantaneous and quantitative reaction to 1 + and 2 occurred when ferrocene (1) and the N-oxopiperidinium hexafluorophosphate 2 + were mixed. These catalytic oxidative conditions were applied to asymmetric tandem lithium amide conjugate addition/radical cyclization/oxygenation sequences leading to the tetrasubstituted pyrrolidines 5 and 6 ( Table 1).…”