Mild Deoxygenation of Aromatic Ketones and Aldehydes over Pd/C Using Polymethylhydrosiloxane as the Reducing Agent

Abstract

Herein, a practical and mild method for the deoxygenation of a wide range of benzylic aldehydes and ketones is described, which utilizes heterogeneous Pd/C as the catalyst together with the green hydride source, polymethylhydrosiloxane. The developed catalytic protocol is scalable and robust, as exemplified by the deoxygenation of ethyl vanillin, which was performed on a 30 mmol scale in an open-to-air setup using only 0.085 mol % Pd/C catalyst to furnish the corresponding deoxygenated product in 93 % yield within 3 hours at room temperature. Furthermore, the Pd/C catalyst was shown to be recyclable up to 6 times without any observable decrease in efficiency and it exhibited low metal leaching under the reaction conditions.

Dual Metal–Acid Pd-Br Catalyst for Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural (HMF) to 2,5-Dimethylfuran at Ambient Temperature

“…However, the CC bond in the furan ring is stabilized by aromatic conjugation, which makes the situation different. 58 It results in the formation of different by-products like MTHFA, BHMTF, etc. The by-product formation can also lead to catalyst deactivation.…”

“…25 The homogeneous acids provide intimacy of acid sites around the metal surface, which could protonate the substrate hydroxyl group and polarize the C−O bond and favor the cleavage of the C−O bond over Pd. 58 However, the addition of homogeneous organic or inorganic acid at the same time could result in the side self-condensation of HMF, which lowers the DMF productivity. 34 In addition, the presence of liquid acids in the reaction mixture leads to the corrosion of equipment.…”

Enantioselective Three‐Component Coupling of Heteroarenes, Cycloalkenes and Propargylic Acetates

“…Additionally, both the allene and heterocyclic ring of indole were cleaved by ozone to give diketone 7 c. [22] Both aromatic ketone groups were then deoxygenated to give 7 d via Pd/C-catalyzed reduction using polymethylhydrosiloxane (PMHS). [23] In summary, we report herein a three-component difunctionalization of cycloalkenes using propargylic electrophiles and heteroarenes such as indoles, pyrroles and some activated furans and thiophenes. Asymmetric Wacker-type attack of nucleophilic heteroarenes on cycloolefins without the aid of a directing group proceeds with excellent stereocontrol.…”

Chemoselective Reductive Deoxygenation and Reduction of α‐Keto Amides by using a Palladium Catalyst

“…Very recently, Adolfsson et al. reported the deoxygenation of aromatic ketones and aldehydes over Pd/C using PMHS as the reducing agent 10b. Generally, the keto group undergoes reductive deoxygenation by Clemensen11 or Wolff–Kishner12 reduction but both of them require harsh reaction conditions.…”