Palladium-Catalyzed Anti-Markovnikov Oxidation of Aromatic and Aliphatic Alkenes to Terminal Acetals and Aldehydes

Abstract

Catalytic anti-Markovnikov (AM) oxidation of terminal alkenes can provide terminally oxyfunctionalized organic compounds. This short review mainly summarizes our recent progress on the Pd-catalyzed AM oxidations of aromatic and aliphatic terminal alkenes to give terminal acetals (oxidative acetalization) and aldehydes (Wacker-type oxidation), along with related reports. These reactions demonstrate the efficacy of the PdCl2(MeCN)2/CuCl/electron-deficient cyclic alkenes/O2 catalytic system. Notably, electron-deficient cyclic alkenes such as p-benzoquinones (BQs) and maleimides are key additives that facilitate nucleophilic attack of oxygen nucleophiles on coordinated terminal alkenes and enhance the AM selectivity. BQs also function to oxidize Pd(0) depending on the reaction conditions. Several other factors that improve the AM selectivity, such as the steric demand of the nucleo­philes, slow substrate addition, and halogen-directing groups, are also discussed.1 Introduction2 Anti-Markovnikov Oxidation of Aromatic Alkenes to Terminal Acetals­3 Anti-Markovnikov Oxidation of Aromatic Alkenes to Aldehydes4 Anti-Markovnikov Oxidation of Aliphatic Alkenes to Terminal Acetals­5 Anti-Markovnikov Oxidation of Aliphatic Alkenes to Aldehydes6 Conclusion

Introducing Type Ⅲ Metal Complex-Stabilized Olefin Radical Cation Induced Addition: A New Mechanism for Palladium-Catalyzed Wacker-Type Oxidation of Terminal Alkenes

“…[22][23][24] AM product aldehydes could also be selectively obtained under the optimized Tsuji-Wacker conditions and the synthetic impact of the aldehydes was later demonstrated 25,26 . Due to the strong potential to be directly transformed into various functional groups under mild conditions in organic synthesis, exploration for practical Wacker-type oxidation methods with excellent AM control has received much attention, and remarkable progress has been achieved in the recent decade [27][28][29][30] Mechanistic studies [31][32][33][34] including experimental investigations and computation calculations were both extensively explored in the past decades for the Wacker process. Evidences showed that the Wacker process is quite sensitive to and dependant on reaction conditions, and subtle changes in experimental conditions could result in substantially different reaction mechanisms; and a "true" pathway with a clear role of CuCl2 is not yet possible to be described.…”

Copper-catalyzed radical oxyallylation of olefins for the construction of alkene-containing isoxazolines

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Among them, the oxyallylation of alkenes is a particularly useful reactions, because the alkenes motif in the resulting products offer rich possibilities for synthetic manipulations. Despite significant advances in the oxyfunctionalization of alkenes, [17][18][19][20][21][22][23][24][25][26] oxyallylation of alkenes have been little explored. France and co-workers developed the palladium-catalyzed oxyallylation of unactivated alkenes using phenols, alcohol and carboxylic acid as the nucleophiles (Scheme 1a).…”

Realization of Anti‐Markovnikov Selectivity in Pd‐Catalyzed Oxidative Acetalization and Wacker‐Type Oxidation of Terminal Alkenes

“…The Pd/Cu‐catalyzed Wacker‐type oxidation is a well‐known reaction that produces carbonyl compounds from alkenes [1–21] . This method, which involves the conversion of ethylene into acetaldehyde, was once an industrial method for the production of acetaldehyde [22] .…”

“…When terminal alkenes other than ethylene are used as substrates, ketones are generally obtained as the main products rather than aldehydes (Scheme 1). Thus, the Wacker‐type oxidation of terminal alkenes proceeds preferentially with Markovnikov selectivity, and the realization of anti‐Markovnikov (AM) selectivity poses a significant challenge [5,6,8,11,13,15–19,21] …”

“…Thus, the Wacker-type oxidation of terminal alkenes proceeds preferentially with Markovnikov selectivity, and the realization of anti-Markovnikov (AM) selectivity poses a significant challenge. [5,6,8,11,13,[15][16][17][18][19]21] There are several types of substrates that afford AM products, including alkenes with directing groups such as oxygen or nitrogen functionalities (allylic ethers, allylic esters, homoallylic alcohols, homoallylic ethers, homoallylic esters, allylic amines, allylic amides, allylic phthalimides etc.) and dienes.…”