Katalytische, aerobe Oxidation von C(sp³)‐H‐Bindungen

Abstract

Oxidationsreaktionen sind eine Schlüsseltechnologie in der Umwandlung von Rohstoffen aus Erdöl zu Substanzen höherer Oxidationsstufen, von denen ausgehend weitere Umsetzungen möglich sind. Diese Oxidationsprozesse nutzen meist molekularen Sauerstoff im letzten Schritt, da dieser im Großmaßstab typischerweise das einzige wirtschaftliche Oxidationsmittel darstellt. Die so hergestellten Basischemikalien weisen üblicherweise kaum funktionelle Gruppen auf und sind zudem meist hoch symmetrisch, weshalb die Frage nach der Selektivität oft keine Rolle spielt. Dagegen werden bei der Herstellung von Feinchemikalien noch immer klassische Oxidationsmittel bevorzugt. Für die Entwicklung nachhaltigerer Produktionsprozesse ist der Einsatz von Sauerstoff eine logische Wahl. Wegen der zahlreichen funktionellen Gruppen und der Komplexität von Feinchemikalien ist das Erreichen von Regio‐ und Chemoselektivität hier besonders anspruchsvoll. Dieser Aufsatz präsentiert die wichtigsten derzeitigen katalytischen Systeme zur aeroben Oxidation sowie die aktuellen Erkenntnisse über die jeweiligen Reaktionsmechansimen.

Selective cleavage of Cα–Cβbonds in lignin models using a bifunctional pyridinium photocatalystviaa PCET process

“…Significantly, when using atmospheric oxygen as an oxidant, little decay in conversion indicates the strong ability of the PTP-dq + -based photocatalytic system to utilize the low-oxygen atmosphere, which increases the advantages of low-cost and sustainability, as well as safety concerning the flash point flammability of organic solvents. 36 The conversion efficiency of 1 is reduced to a certain extent when the anion is replaced by heavy atoms (Br − or I − ), but it is beneficial for improving the selectivity of 2 . The yield and selectivity reached 90% and 94%, respectively, after about 1.5 hours of irradiation when using PTP-dq·Br as the photocatalyst (Fig.…”

Thiosulfonates as Emerging Reactants: Synthesis and Applications

“…Finally,non-toxic molecular oxygenisc onsidered as the ideal green oxidant [36] for the oxidation of disulfides (3). After all, such methods built in both oxygen atoms of O 2 in the product, which is reflected in a 100% AE.…”

Iridium‐Catalyzed Direct C4‐ and C7‐Selective Alkynylation of Indoles Using Sulfur‐Directing Groups

“…This reaction was also applicable to 2,3-dialkylindoles,w hich are considerably sensitive to oxidative conditions.A ctually,t he alkynylated product 9k slowly oxidized into the corresponding diol (9k-diol) [12] and diketone (9k-dione)byexposure to air [14] (for details,see the Supporting Information). Thep resence of competitive directing groups at the C3position did not interfere with the regioselectivity of this transformation, giving the C7-alkynylated indoles exclusively.…”

“…In contrast, C6-substituted indoles were unreactive under the standard reaction conditions,p robably because of the steric hindrance (not shown). This reaction was also applicable to 2,3-dialkylindoles,w hich are considerably sensitive to oxidative conditions.A ctually,t he alkynylated product 9k slowly oxidized into the corresponding diol (9k-diol) [12] and diketone (9k-dione)byexposure to air [14] (for details,see the Supporting Information). Interestingly,t he alkynylation of 1-(methylthio)-2-methylindole (8l)resulted in the formation of 9l in 71 %yield with spontaneous 1,3-migration of the SMe group, and the structure was confirmed by X-ray analysis.…”