Reaktionen der Carbonylgruppe fluorierter Ketone

Abstract

Neuerdings wird der Chemie polyfluorierter Ketone große Beachtung geschenkt. Die fluorierten Ketone und ihre Imine reagieren an der Carbonyl‐ oder Iminogruppe in vielseitiger Weise. Insbesondere die elektronenziehenden Perfluoralkylgruppen verstärken die elektrophilen und schwächen die nucleophilen Eigenschaften der Carbonylgruppe. Außerdem erschweren Perfluoralkylgruppen die heterolytische Abspaltung der Hydroxygruppe von Anlagerungsprodukten indem sie die Stabilität der Carbonium‐Ionen erniedrigen. Die verstärkte Elektrophilie der Carbonylgruppe und die erhöhte Stabilität der Anlagerungsprodukte führt nicht nur zur Änderung der Reaktionsfähigkeit in den charakteristischen Keton‐Reaktionen, sondern auch zu zahlreichen neuen Reaktionen, die bei nicht fluorierten Ketonen nicht beobachtet werden. Perfluorierte Ketone geben damit die Möglichkeit, sehr verschiedenartige fluororganische Verbindungen zu synthetisieren.

Ketone–Alcohol Hydrogen‐Transfer Equilibria: Is the Biooxidation of Halohydrins Blocked?

“…Initial rates of the LBADH‐catalyzed HT of ketones 2 b–h : At this point, we were intrigued by the question of why ketones bearing EWGs oxidized i PrOH more efficiently. As already mentioned, this behavior has been associated with the higher electrophilicity of the carbonyl carbon in this type of compound,16 which should be reflected in the kinetics of the reaction. Accordingly, we measured the initial velocities ( V 0 ) of the LBADH‐catalyzed reduction of ketones 2 c – h (see the Supporting Information for details) and calculated their ratio with respect to the parent substrate ( 2 b ; Figure 2).…”

“…Ketones bearing electron‐withdrawing groups (EWGs) are tacitly regarded as electron‐deficient ketones and, thus can be more readily attacked by nucleophiles (e.g., hydride) than “non‐activated” ketones, which would lead to higher reduction rates. On the other hand, it has also been argued that α‐halo substituents increase the stability of the corresponding alcohols by destabilizing the partial positive charge formed during their oxidation,16 which leads to an increase in the activation energy for the oxidation of halohydrins. These aspects are in favor of both a kinetic blockade of the oxidation of this kind of alcohol and the commonly accepted fact that the Oppenauer oxidation of alcohols is under thermodynamic control, that is, the final composition of the reaction mixture is mostly determined by the reduction potentials of the ketones/aldehydes involved 4…”

The Chemistry of α-Haloketones and Their Utility in Heterocyclic Synthesis

“…Direct fluorination, by using F 2 , often gives rise to side reactions leading to polyfluorinated and degradation products and are therefore of limited use. However, a number of reviews have been published by Erian [ 34 ] and others [ 35 , 36 , 37 ] on the preparation of α-fluoroketones.…”

The Chemistry of α‐Haloketones and Their Utility in Heterocyclic Synthesis

“…Direct fluorination, by using F 2 , often gives rise to side reactions leading to polyfluorinated and degradation products and are therefore of limited use. However, a number of reviews have been published by Erian [34] and others [35][36][37] on the preparation of α-fluoroketones.…”