Trifluoromethanesulfonic Acid-Mediated Reaction of 2-Methoxyacetic Acid with Arenes —Clarification of Reaction Behavior and Route for Diarylmethanes and Anthracene Derivatives Formation—

Abstract

α-Methoxycarboxylic acids 1 undergo decarbonylative α,α-diarylation reaction with arenes 2 in the presence of phosphorus pentoxide-methanesulfonic acid mixture (P₂O₅–MsOH). However, 2-methoxyacetic acid (1d) shows different reaction behavior from those of other α-carboxylic acids (1). Trifluoromethanesulfonic acid (TfOH)-mediated reaction of 2-methoxyacetic acid (1d) with arenes 2 yields anthracene derivatives 10 in addition to Friedel-Crafts acylation type products and diarylmethanes 4. The reaction behavior was elucidated by estimating the influence of the kind of acidic medium and the substrate structure. Furthermore, based on the results of the reaction of the model compounds for the corresponding suspected reaction pathways, the adequacy of the pathways was evaluated. TfOH-mediated reactions of 2-methoxyacetic acid (1d) with arenes except for that with benzene (2f) proved to proceed via α-hydroxyacetophenone homologues 7 and 11, 1,1-diarylethanediol derivatives 14, and 1,2,2-triarylethanol derivative 17.