Direct Allylic Functionalization Through Pd‐Catalyzed C–H Activation

Abstract

After a brief introduction emphasizing the synthetic relevance of the allylic C–H activation step, evoking the first pioneering stoichiometric studies that sowed the “seeds” of this subject, and analyzing similarities and differences between a “classical” and a “direct” Pd‐catalyzed allylation process, this review outlines some selected examples of palladium‐catalyzed direct allylic functionalization. This old reaction, ignored for many years, is now living a new and exciting era.

Palladium‐Catalyzed Regiodivergent Substitution of Propargylic Carbonates

“…[1,2] However, compared to allylic analogues, [3][4] palladium-catalyzedc ouplings of propargyl electrophilesh ave received much less attention.O ne potential reason for the lesser developmento f these couplings is the greater complexity in achieving regioselective and chemoselective substitution (Scheme1). [1,2] However, compared to allylic analogues, [3][4] palladium-catalyzedc ouplings of propargyl electrophilesh ave received much less attention.O ne potential reason for the lesser developmento f these couplings is the greater complexity in achieving regioselective and chemoselective substitution (Scheme1).…”

Steric effect of carboxylic acid ligands on Pd-catalyzed C–H activation reactions

“…Gratifyingly, the yield of 3 significantly increased by elongating one of the methyl substituents of 1i to ethyl (1j: 80%), n-pentyl (1k: 88%) and n-dodecyl (1l: 91%) groups, respectively (entries [10][11][12]. However, the use of 1m…”

“…Among them, Pd catalysis is widely utilized [8][9][10][11][12][13][14]. In these cases, carboxylic acids, typically pivalic acid, play an important role as the ligand in C-H bond activation step via concerted metalation deprotonation (CMD) mechanism [15][16][17].…”

The development and mechanistic investigation of a palladium-catalyzed 1,3-arylfluorination of chromenes

“…We assumed that the 2,1-arylfluorination product was formed in an analogous fashion to our previously reported reaction with styrenes, namely by a migratory insertion that places the palladium in the benzylic position, and the aryl-group in the homo-benzylic position, followed by C–F bond formation. For the 1,3-arylfluorination reaction, we anticipated an oxidative Heck-type mechanism would also be operative, although the possibility of alternative mechanisms, including allylic C–H palladation, 18 was considered. We hypothesized that the 1,3-product was formed by a migratory insertion with the opposite sense of selectivity, followed by palladium migration, and C–F bond formation.…”