PPh3-Assisted Esterification of Acyl Fluorides with Ethers via C(sp3)–O Bond Cleavage Accelerated by TBAT

Abstract

We describe the (triphenylphosphine (PPh3)-assisted methoxylation of acyl fluorides with cyclopentyl methyl ether (CPME) accelerated by tetrabutylammonium difluorotriphenysilicate (TBAT) via regiospecific C–OMe bond cleavage. Easily available CPME is utilized not only as the solvent, but a methoxylating agent in this transformation. The present method is featured by C–O and C–F bond cleavage under metal-free conditions, good functional-group tolerance, and wide substrate scope. Mechanistic studies revealed that the radical process was not involved.

Recent Advances in C–F Bond Activation of Acyl Fluorides Directed toward Catalytic Transformation by Transition Metals, N-Heterocyclic Carbenes, or Phosphines

“…In the first protocol, a series of acyl fluorides was accidentally defluoromethoxylated using PPh 3 as the catalyst and methyl ethers were utilized as a methoxy source to synthesize an array of methyl benzoates with good functional group tolerance (Scheme 49a). 94 In the second protocol, tris(2,4,6-trimethoxyphenyl)phosphine was utilized as both a catalyst and a methoxylating agent to again afford a series of methyl benzoates in good yields (Scheme 49b). 95 After extensive studies, it was concluded that the phosphine forms an acyl phosphonium fluoride from the acyl fluoride, and that regiospecific cleavage of the C-O bond promoted by the acyl phosphonium fluoride is a key step in the reaction.…”