Thallium in Organic Synthesis. 61. Intramolecular Capture of Radical Cations from Thallium(III) Trifluoroacetate Oxidation of Arylalkanoic Acids and Arylalkanols. New Routes to Oxygen Heterocycles

Article abstract of DOI:10.1021/ja00413a013

Treatment of electron-rich arylpropionic acids with TTFA in TFA containing a small amount of BF3*etherate results in the formation of dihydrocoumarins and spirocyclohexadienone lactons by initial formation of aromatic radical cations followed by intramolecular cyclization involving the side-chain carboxyl group.The scope and limitations of this reaction with respect to aromatic substitution and the length of the alkanoic acid side chain have been examined; the reaction has been extended with analogous results to 1-naphthalenylalkanoic acids.Oxidation of a series of homologous phenyl- and naphthalenyl-1-alknols with TTFA under similar conditions results in intramolecular cyclization to give fused or pendant cyclic esters.It is suggested that the observed propensity for intramolecular cyclization may due to complexation of both the aryl group and the side-chain basic substituent (-COOH or -OH) with thallium(III).