Effects of Silver Carbonate and p-Nitrobenzoic Acid for Accelerating Palladium-Catalyzed Allylic C-H Acyloxylation

Semipinacol Rearrangement of Iododifluorohomoallyl Alcohols and Its Application in the Allylic C-H Esterification Reactions

We herein present a study on the Ag(I)-mediated semipinacol rearrangement of iododifluorohomoallyl alcohols, the resulting allylic difluoromethyl ketones underwent oxidative allylic C-H esterification under palladium catalysis in the absence of external ligand. This process yielded a range of difluoromethyl ketones derived from allyl esters in a single operation. The reaction features broad scope of o-nitrobenzoic acids and homoallylic iododifluoroalcohols affording the targeted molecules in synthetically useful yields. Control experiments illustrated that the silver salt acted as not only a Lewis acid to promote the cleavage of a C-I bond and furnish the semipinacol rearrangement but also a co-oxidant in the catalytic cycle for the allylic C-H esterification.

Enantioconvergent Palladium-Catalyzed Alkylation of Tertiary Allylic C-H Bonds

Enantioconvergent catalysis enables the conversion of racemic molecules into a single enantiomer in perfect yield and is considered an ideal approach for asymmetric synthesis. Despite remarkable advances in this field, enantioconvergent transformations of inert tertiary C-H bonds remain largely unexplored due to the high bond dissociation energy and the surrounding steric repulsion that pose unparalleled constraints on bond cleavage and formation. Here, we report an enantioconvergent Pd-catalyzed alkylation of racemic tertiary allylic C-H bonds of α-alkenes, providing a unique approach to access a broad range of enantioenriched γ,δ-unsaturated carbonyl compounds featuring quaternary carbon stereocenters. Mechanistic studies reveal that a stereoablative event occurs through the rate-limiting cleavage of tertiary allylic C-H bonds to generate σ-allyl-Pd species, and the achieved E/Z-selectivity of σ-allyl-Pd species effectively regulates the diastereoselectivity via a nucleophile coordination-enabled SN 2'-allylation pathway.