Palladium‐Catalyzed Oxidation Reactions of Alkenes with Green Oxidants

Abstract

Transition‐metal‐catalyzed oxidative functionalization of alkenes has emerged as a powerful and valuable tool in modern organic synthesis. Recently, many methods have been established for the assembly of C−C and C–heteroatom bonds, which provides tremendous possibility for application in biology, medicine, and materials science. However, the use of stoichiometric amounts of strong oxidants leads to poor selectivity, low atom economy, and a series of undesired waste products. By contrast, green oxidants, such as O2, H2O2, or tert‐butyl hydroperoxide (TBHP), have bright prospects due to their attributes of mild, low cost, and great sustainability in transition‐metal‐catalyzed oxidation reactions. Based on the great and unique potential for the development of aerobic reactions, this review mainly highlights homogenous palladium‐catalyzed green oxidations of alkenes that have been reported in recent years. These methods provide new strategies for the transformation and functionalization of alkenes; some of them have also been successfully applied to the synthesis of the core structures of drugs and natural products. Additionally, through in‐depth studies of the reaction mechanisms in this field, it is believed that palladium‐catalyzed green oxidation reactions of alkenes with O2, H2O2, or TBHP will create added value for organic synthetic chemistry.

Palladium‐Catalyzed Cascade Cyclization/Alkynylation Reactions

“…In this respect, Cacchi and coworkers disclosed ap alladium-catalyzed "one-pot" domino process for the formation of 3-alkynylindoles (20)f rom 2-alkynyltrifluoroacetanilides (19)w ith bromoalkynes (Scheme 12). [31] The alkynylationsc an be carried out with 5mol %P d(PPh) 4 in MeCN at 60 8Cint he presence of 3equiv of Cs 2 CO 3 or K 2 CO 3 as ab ase under an argon atmosphere.B oth electron-donating and electron-withdrawing bromoalkynes were perfectly accommodatedu nder the optimized reaction conditions. Unfortunately,1-iodophenylacetylene was not compatible with the optimizedc onditions, which probablyt endency to undergo side reactions in the presence of transition metal catalysts.…”

“…[3] Noteworthy,t he outstanding features of palladium-catalyzed chemicalt ransformations are the diversity of bond-forming types, excellent chemical and stereoselectivities, andg ood functional groups compatibilities. [4] Therei so ne thing worth mentioning, the palladium-catalyzedc hemical transformations have been widely application in both academic research and industrial production.…”

Palladium Catalysis for Aerobic Oxidation Systems Using Robust Metal–Organic Framework

“…Communications pressure O 2 atmosphere within the framework, thus enhancing the electron-transfer efficiency between O 2 and Pd 0 , as high-pressure O 2 has been evidenced to increase the reoxidation rate of Pd 0 in homogeneous systems. [13] Additionally, when UiO-67-phen-Pd/Cu(1:2) was utilized under anaerobic conditions, an obviously reduced yield was observed (entry 13). XPS investigation of this recovered catalyst was conducted to prove the change of valence state of Cu and Pd species (Figures 1 d,e).…”

Aerobic Heterogeneous Palladium-Catalyzed Oxidative Allenic C−H Arylation: Benzoquinone as a Direct Redox Mediator between O 2 and Pd

“…6,7 Palladium-catalyzed aerobic oxidations play an indispensable role in organic synthesis. [8][9][10][11][12] However, the direct reoxidation of in situ-formed low valent Pd(0) by ambient O 2 is generally considered kinetically unfavorable, and often leads to Pd(0) aggregation and Pd black formation. 13 One way to avoid this problem has been to use air-stable ligands that can stabilize Pd(0) and restrain its aggregation.…”