Palladium‐Catalyzed Aerobic Synthesis of Terminal Acetals from Vinylarenes Assisted by π‐Acceptor Ligands

Abstract

What prompted you to investigate this topic? We have recently found that the addition of electron-deficient cyclic alkenes, such as maleimide, accelerates ap alladium-cata-lyzed anti-Markovnikov Wacker-type oxidation of vinylarenest o arylacetaldehydes using O 2 .W ee xpected that this method could be applied to other reactions related to the anti-Markov-nikov Wacker-type oxidation, such as the one presented in this paper.The electron-deficient cyclic alkenesw ould operate as li-gands for palladium to accelerate the reactiona sw ella ss tabi-lize the in situ formed Pd 0 species, suppressing deactivation.

Palladium/Copper‐catalyzed Oxidation of Aliphatic Terminal Alkenes to Aldehydes Assisted by p‐Benzoquinone

“…As an additive, BQ gave the best results among the electron‐accepting ligands examined in terms of the total yield of aldehydes (see Table S3). These included BQ derivatives, maleic anhydride, maleimide, acyclic α,β‐unsaturated carbonyl compounds, and CO, some of which are known to enhance the catalytic activity and/or anti‐Markovnikov selectivity in the Pd/Cu‐catalyzed aerobic oxidation of aromatic alkenes to aldehydes and terminal acetals, as well as the oxidation of aliphatic alkenes to terminal acetals . The absence of H 2 O or the use of 2.0 equiv.…”

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

“…Kinetic experiments were performed to shed light on the reaction mechanism. 41 The reaction orders for pinacol and PdCl 2 (MeCN) 2 were estimated to be 0 and 1, respectively. Based on the kinetics data, a plausible mechanism is illustrated in Scheme 13.…”

“…Further investigation revealed that molecular oxygen could be employed as a terminal oxidant, combined with CuCl and an electron-deficient cyclic alkene as co-catalysts (Table 1). 41 Bulky t-AmylOH was used as the solvent. Methoxyp-benzoquinone (MeOBQ) and N-phenylmaleimide were efficient (entries 4, 5, and 9) among the cyclic alkenes examined, including BQs, maleic anhydride, and maleimides.…”

“…42 The activation parameters [ΔH ‡ = (8.7 ± 0.8) kcal mol -1 and ΔS ‡ = (-49 ± 3) cal mol -1 K -1 ] were derived from the Eyring plot for the reaction of styrene with pinacol. 41 The large negative ΔS ‡ value suggests that the rate-limiting step is the nucleophilic attack of t-AmylOH on the coordinated styrene.…”

Synthesis of Arylacetaldehydes by Iridium‐Catalyzed Arylation of Vinylene Carbonate with Arylboronic Acids

“…[1] Approaches to the arylacetaldehydes [2] are classified into two reaction types:O ne is functional group transformation of compounds bearing Ar-C-C carbon skeleton (Type 1, Scheme 1a), and the other is carbon-carbon bond formation by introduction of af ormyl group into an arylmethyl unit or introduction of af ormylmethyl group (or its synthetic equivalent) into an aryl unit constructing the Ar-C-C skeleton (Type 2, Scheme 1b). Selective partial oxidation of alcohols [3] and partial reduction of carboxylic acids [4] are common Ty pe 1r outes to arylacetaldehydes.O xidation of styrene derivatives [5,6] and hydration of arylacetylenes, [7,8] which are catalyzed by late transition metals,h ave been also reported to produce arylacetaldehydes.O ft he Ty pe 2r eactions,o ne-carbon homologation of aromatic aldehydes [9] and formylation of benzylic halides [10] are typical examples.F or the synthesis of arylacetaldehydes through two-carbon extension, the Mizoroki-Heck type reaction of aryl halides with vinyl alkyl ethers catalyzed by apalladium complex giving balkoxystyrenes has been the most extensively studied;h ere, the efforts for higher linear/branch selectivity have been made mainly by modifying the alkyl moiety of the vinyl alkyl ethers and screening the solvents. [11] Palladium-catalyzed cross-coupling of aryl halides with b-alkoxyvinylmetals is another way to produce b-alkoxystyrenes by two-carbon extension.…”