Catalytic Allylic C−H Acetoxylation and Benzoyloxylation via Suggested (η³-Allyl)palladium(IV) Intermediates

Abstract

Palladium-catalyzed allylic acetoxylations and benzoyloxylations were carried out using iodonium salts. The reactions proceed under mild conditions with high regio- and stereoselectivity. The catalysis can be performed under both acidic and nonacidic conditions without use of BQ or other external oxidants and activator ligands. Deuterium labeling experiments clearly show that the catalytic reaction proceeds through (eta(3)-allyl)palladium intermediates. A stoichiometric study with one of the catalysts provided evidence for the formation of a Pd(IV) species.

Bis-N-heterocyclic Carbene Palladium(IV) Tetrachloride Complexes: Synthesis, Reactivity, and Mechanisms of Direct Chlorinations and Oxidations of Organic Substrates

“…In order to understand the transfer of Cl + from LPd IV Cl 4 to π-systems, we studied the reaction of 7 and 7·Cl − with alkenes in more detail. Interactions of isolated Pd IV -compounds with alkenes or alkynes have never been studied, even though the existence of (η 2 -alkene/alkyne)Pd IV -complexes was proposed in Heck-reactions 42, 66 and other carbopalladations, 67 allylic C-H acetoxylations 68 , and cyclotrimerisations. 69 …”

Mechanistic Investigation of Palladium-Catalyzed Allylic C–H Activation

“…28,30 For allylic C−H oxidation, White and coworkers have suggested that a carboxylate counterion on palladium is needed to effect C−H cleavage. 31 A carboxylate anion also plays a key role in the C−H activation step of the proposed Pd(II)/Pd(IV) catalytic cycle for an allylic C−H acetoxylation 32 or as a base in a recently published allylic acyloxylation. 33 Similarly, for allylic aminations, a carboxylate anion has also been suggested to be involved in the cleavage of the C−H bond.…”

Aerobic Acyloxylation of Allylic C−H Bonds Initiated by a Pd0 Precatalyst with 4,5‐Diazafluoren‐9‐one as an Ancillary Ligand

“…Pd(OAc) 2 is one of the most common commercially available Pd II sources and, therefore, is the most prevalent Pd source for allylic oxidation, among other reactions . Szabó and co‐workers reported two strategies for acyloxylation catalyzed by Pd(OAc) 2 : (a) using 4 equivalents of carboxylic anhydride or (b) incorporating the carboxylate source into their oxidant by utilizing 3–3.5 equivalents of a hypervalent iodine oxidant with the corresponding lithium carboxylate salt . Hartwig and co‐workers used stoichiometric tert ‐butylbenzoyl peroxide and Pd II benzoate to form allyl benzoates, reducing carboxylate loading to 2 equivalents .…”