Asymmetric catalysis, part 108 copper catalysts with optically active ligands in the enantioselective Meerwein arylation of activated olefins

Intermolecular Olefin Functionalisation Involving Aryl Radicals Generated from Arenediazonium Salts

“…Like in the generally accepted mechanism for the Meerwein arylation, [36,37] copper ions play a double role in the cyanoarylation presented in Scheme 5. At the beginning, copper(I) acts as reductant for the diazonium salt 7 initiating its decomposition to the aryl radical and nitrogen.…”

“…The halogen-transfer step itself has been proposed to proceed either by a radical atom transfer or through an alkylcopper intermediate that undergoes reductive elimination. [37,79] In the early procedures, a previously diazotised aniline was added as arenediazonium halide to a water-acetone solution containing the olefinic substrate and a copper(II) halide as catalyst. Following this protocol, phenyldiazonium chloride (1) and acrolein (46) can conveniently be converted to 2-chloro-3-phenylpropionaldehyde (47) (Scheme 15).…”

The Diaryl(oxy)methyl Group: More than an Innocent Bystander in Chiral Auxiliaries, Catalysts, and Dopants

“…Although the diphenyl(oxy)methyl group is not a typical structural motif in catalysis by late‐transition metals, it was found to have a beneficial effect on the enantioselectivity in a rhodium‐catalyzed hydrosilylation in the presence of pyridinyloxazolines,41a in bisoxazoline‐mediated Meerwein arylation reactions of activated alkenes41b as well as in allylic alkylation41c and hydroformylation reactions 41d. Cyclic phosphites, phosphoramidites, and phosphonites with a TADDOL backbone are also suitable ligands for late transition metals 8a.…”

Nitrogen-Centered Radical Scavengers

“…Attempts towards the development of enantioselective versions of the Meerwein arylation are rare in the literature. 44 In a recent diastereoselective approach, the stereochemistry at the newly formed quaternary carbon center was controlled by a chiral backbone including a cyclohexane-1,2-diol moiety (Scheme 27). 45 Because of the C 2 symmetry of the bisdiazonium salt 107, it is not important which of the two diazonium units is reduced first to give an aryl radical, and which one later acts as the radical scavenger.…”