Palladium-Catalyzed γ-Selective and Stereospecific Allyl−Aryl Coupling between Acyclic Allylic Esters and Arylboronic Acids

Abstract

Reactions between acyclic (E)-allylic acetates and arylboronic acids in the presence of a palladium catalyst prepared from Pd(OAc)(2), phenanthroline (or bipyridine), and AgSbF(6) (1:1.2:1) proceeded with excellent gamma-selectivity to afford allyl-aryl coupling products with E-configuration. The reactions of alpha-chiral allylic acetates took place with excellent alpha-to-gamma chirality transfer with syn stereochemistry to give allylated arenes with a stereogenic center at the benzylic position. The reaction tolerated a broad range of functional groups in both the allylic acetates and the arylboronic acids. Furthermore, gamma-arylation of cinnamyl alcohol derivatives afforded gem-diarylalkane derivatives containing an unconjugated alkenic substituent. The synthetic utility of this method was demonstrated by its utilization in an efficient synthesis of (+)-sertraline, an antidepressant agent. The observed gamma-regioselectivity and E-1,3-syn stereochemistry were rationalized based on a Pd(II) mechanism involving transmetalation between a cationic mono(acyloxo)palladium(II) complex and arylboronic acid, and directed carbopalladation followed by syn-beta-acyloxy elimination. The results of stoichiometric reactions of palladium complexes related to possible intermediates were fully consistent with the proposed mechanism.

Gas-phase studies of metal catalyzed decarboxylative cross-coupling reactions of esters

“…3). Sawamura has recently summarized the range of mechanisms that can operate (Scheme 6) [34]. Importantly, the reaction mechanism followed dictates the regiochemical and stereochemical outcomes for non-symmetric allyl acetate substrates.…”

“…Sawamura developed a new γ-selective strategy that entirely avoids the issue of isomerization of the allylmetal species a b c d Scheme 6 Mechanisms for the metal catalyzed allylic alkylation reactions of ester substrates. Adapted from [34].…”

“…3). For example, allylic alkylation reactions have fascinated organic chemists in terms of their regiochemical and stereochemical outcomes [28][29][30][31][32] as well as for the diverse range of possible mechanisms [33][34][35][36]. Unfortunately the R 1 group of the carboxylate is wasted in these reactions.…”

Palladium-Catalyzed Heck-Type Coupling of Allyl Esters: β-Hydride versus β-Acetoxy Elimination

“…32b The substrate scope of this reaction was later expanded to various allyl esters by Sawamura's group, 33 and for this synthesis Pd(OAc) 2 , 1,10-phenanthroline, and silver(I) hexafluoroantimonate (AgSbF 6 ) (1:1.2:1) were employed as the catalytic system. Reactions between acyclic (E)-allyl esters and arylboronic acids proceeded with excellent g-selectivity producing allyl-aryl coupling products with E-configuration under these conditions.…”

Development of Batch and Flow Immobilized Catalytic Systems with High Catalytic Activity and Reusability

“…While there are numerous reports on aryl-aryl coupling with aryl boron reagents (Suzuki-Miyaura reaction), little attention has been paid to the more challenging allyl-aryl coupling (allylic arylation), which often requires a relatively high reaction temperature with a large amount (1-10 mol%) of catalyst. [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] Therefore, the newly developed catalyst MPPI-Pd should be applied to the allylic arylation to provide high catalytic activity, reusability and substrate tolerance.…”