Palladium Complex Catalyzed Acylation of Allylic Esters with Acylsilanes

Abstract

Acylation of allylic esters (2) with acylsilanes (1) in the presence of a catalytic amount (5 mol %) of a palladium complex is reported. The reaction proceeds selectively to afford beta,gamma-unsaturated ketones (3) in high yields. [Pd(eta3-C6H5CH=CHCH2)(CF3COO)]2 (4a) showed the best catalytic activity. After the reaction, formation of CF3COOSiMe3 (5a) was confirmed by 29Si NMR measurement of the resulting reaction mixture, indicating the trimethylsilyl moiety effectively traps the CF3COO leaving group from 2. The leaving group of the allylic esters affects the reaction considerably: allylic trifluoroacetate gave the best result, while the corresponding acetates and trichloroacetates did not afford any acylation products at all. Stoichiometric reaction of 4a with 1 gave acylation product 3 with a formation of 5a and Pd(0), whereas no acylation reaction took place with the corresponding acetate complex [Pd(eta3-C6H5CH=CHCH2)(CH3COO)]2 (4b). A DFT calculation suggests that interaction of high-lying HOMO of 1 and low-lying LUMO of eta3-allylpalladium trifluoroacetate intermediate 4 would be indispensable in the catalytic cycle.

Synthesis of Acylsilanes by Copper(I)‐Catalyzed Addition of Silicon Nucleophiles onto Acid Derivatives

“…[4] New types of catalysts have also been developed with regard to the activation of acylsilanes in 1,2-benzointype additions and 1,4-Stetter reactions, e.g., thiazolium salts, [5] cyanides [6] and metallophosphites. [7] More recently, new applications of acylsilanes have been established with the addition of enolates, [8] Pd-catalyzed coupling reactions, [9] synthesis of substituted g-lactams, [10] or photochemical transformations.…”

Palladium-Catalyzed Intermolecular Oxidative Amination of Alkenes with Amines, Using Molecular Oxygen as Terminal Oxidant

“…To confirm the participation of the η 3 -allylpalladium intermediate as the key in the catalytic cycle, and in order to obtain further insights into the specific role of the Pd(OCOCF 3 ) 2 catalyst in this reaction, the (η 3 -cinnamyl)palladium trifluoroacetate dimer (7) and (η  -cinnamyl)palladium acetate dimer (8) were synthesized independently as model intermediates, according to the literature methods [61,62]. Stoichiometric reactions with diphenylamine (1) were carried out under the conditions shown in Equation 5, using the complexes 7 and 8.…”

Retracted: Direct Allylation of In Situ Generated Aldehyde Acyl Anions by Synergistic NHC and Palladium Catalysis

“…[6] The development of a straightforward, catalytic, and milder process would directly provide an efficient access to b,g-unsaturated ketones, which are frequently observed in natural products and biologically active compounds. [5,8,9] They have been used also for the synthesis of fine chemicals and complex structures. [5,8,10] In view of their importance and the contemporary interest, many methods for their synthesis have been reported recently, starting from various other substrates.…”

“…[5,8,9] They have been used also for the synthesis of fine chemicals and complex structures. [5,8,10] In view of their importance and the contemporary interest, many methods for their synthesis have been reported recently, starting from various other substrates. [9][10][11] We envisioned (Scheme 2) that after umpolung, which is achieved in situ by a catalytic amount of an N-heterocyclic carbene (NHC), the aldehyde would react as a nucleophile with the electrophilic p-allylpalladium complex to furnish the desired C-allylated product, the b,g-unsaturated ketone.…”