Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Seit Februar 2021 bietet Wolfgang Brandt, ehemaliger Leiter der Arbeitsgruppe Computerchemie am IPB, sein Citizen Science-Projekt zur Pilzbestimmung an. Dafür hat er in regelmäßigen Abständen öffentliche Vorträge zur Vielfalt…
The reduction of prochiral ketones has been performed by Cr(II) L-amino acid complexes in aqueous DMF solution under mild conditions in good yields and moderate (up to 58%) ee values. The dependence of the yield and enantioselectivity on various factors such as the structure of the ligand, pH and the solvent has also been investigated. A mechanism based on SET from the Cr(II) ion followed by protonation by water and the formation of an organochromium intermediate is also proposed.
Publikation
Schrekker, H.; Micskei, K.; Hajdu, C.; Patonay, T.; de Bolster, M.; Wessjohann, L.;Involvement of an Oxidation-Reduction Equilibrium in Chromium-Mediated Enantioselective Nozaki–Hiyama ReactionsAdv. Synth. Catal.346731-736(2004)DOI: 10.1002/adsc.200404021
Ligand induced enantioselective versions of the chromium(II)‐mediated Nozaki–Hiyama reaction to homoallyl alcohols proved to be very difficult to achieve, especially if any other nucleophile than the parent allylchromium(III) species was applied. Also, the reaction is frequently accompanied by the formation of oxidation side products, predominantly allyl ketones. This can be explained by an Oppenauer–(Meerwein–PonndorfVerley) type mechanism (OMPV reaction). The addition of an enantiopure ligand to racemic chromium homoallyl alcoholate intermediates produced enantiomerically enriched homoallyl alcohols with an enantiomeric excess of up to 32%. This observation not only supports that the proposed OMPV oxidation‐reduction equilibrium plays a crucial role in Nozaki–Hiyama reactions, but also proves its involvement in enantioselective versions.