Alkoxides as nucleophiles in (.pi.-allyl)palladium chemistry. Synthetic and mechanistic studies

Abstract

A new methodology for the use of alkoxides as nucleophiles in (ir-allyl)palladium chemistry has been developed. In this process an allylic alcohol serves as the precursor to the ir-allyl complex and a triethylsilyl (TES) ether as precursor to the alkoxide nucleophile. By using Pd(PPh3)4 in CC14, PPh3Cl+CCl3" is generated transposing the ROH into an oxyphosphonium group, R-0-P+Ph3, and liberating Cl". The Cl deprotects the TES ether, providing the nucleophile in situ. Application of this reaction to the preparation of a variety of furans is discussed. This process was determined to proceed with overall predominant retention of configuration. Mechanistic studies suggest a small energy difference between attack by alkoxide on the allyl ligand of the intermediate complex and attack on the metal, followed by reductive elimination.

C(sp3)O Bond‐Forming Reductive Elimination of Ethers from Bisphosphine‐Ligated Benzylpalladium(II) Aryloxide Complexes

“…Reactions that occur by dissociation of aryloxide ligands to form ionic intermediates during organometallic processes in nonpolar solvents are unusual. Nucleophilic attack of phenoxide onto a p-bound allyl ligand is known, [23][24][25][26] but none of the reported reactions begin with an allylalkoxide complex.…”

Palladium‐Catalyzed Formation of Cyclic Ethers – Regio‐, Stereo‐ and Enantioselectivity of the Reaction

“…[a] Laboratoire de Synthèse Asymétrique, associé au CNRS, UMR 5181, CPE Lyon, Université Pd 0 -catalyzed intramolecular heteroannulation through allylic alkylation, the so-called Tsuji-Trost reaction, generally employs allylic acetates, [7][8][9][10][11] benzoates, [12] carbonates, [13][14][15][16] or vinyl epoxides [8,17,18] bearing a hydroxy group. Allylsilanes have also been used as precursors of the η 3 -allyl intermediates, starting from PdCl 2 and CuCl 2 , affording the corresponding THF derivatives in quite good yields.…”

Lewis Acid-Catalyzed Propargylic Etherification and Sulfanylation from Alcohols in MeNO2-H2O

“…In contrast, 2°alcohols such as cyclopentanol and cyclohexanol afforded 2ad and 2ae (entries 3 and 4). Surprisingly, both 1°and 2°alcohols are also nucleophilic toward propargyl cations in MeNO 2 -H 2 O. Alcohols bearing other aromatic substituents at the R 1 -position were examined with the 1°and 2°alcohols (entries [6][7][8][9][10][11][12][13][14][15][16][17]. Alcohol 1d, bearing the bulky aromatic substituent, 2,4,6-trimethylphenyl, also produced propargylic ether 2da in excellent yield (entry 12).…”

“…46) formed the reaction with other thiols such as 2-thienyl, naphthyl, p-chlorophenyl and cyclohexylthiol and obtained satisfactory results (entries 2-5, Table 4). A variety of propargyl alcohols bearing the substituents such as R 1 ϭ2-thienyl, 1-naphthyl and benzodioxol-5-yl produced some propargyl sulphides 8ba-8gc in moderate to high yields (entries [6][7][8][9][10][11]. Surprisingly, Lewis acid-catalyzed C-S bond formation with thiols generally proceeded without further addition of thiols to the alkynyl group, and the desired propargyl sulphides were obtained in good to high yields (entries 1-11).…”

“…However, substitution of hydroxyl group in an alcohol generally requires the prior activation of the hydroxyl group because of the poor leaving ability of this group. 5,6) An alcohol used as a precursor for carbocations is usually activated by transforming it to the corresponding acetate, [7][8][9][10][11][12][13][14][15][16][17] carbonate, 18,19) halide, 20) phosphonate. 21,22) Prior activation of an alcohol is also necessary if it has to be used as a nucleophile because of its low nucleophilicity.…”