Alkylation Triggered an Acylation of Arenes with a Highly Electrophilic Acylphosphonium Salt

Friedel–Crafts acylation is usually promoted by Lewis acids or Brønsted acids. In this work, a novel acylation of arenes with a highly electrophilic acylphosphonium salt was developed. The alkylation of the phosphorus atom in acylphosphines generated a neutral trivalent phosphine as a good leaving group and triggered the high electrophilicity of the acylphosphonium salt. Using acylphosphonium salts, 38 examples of acylations of arenes, alcohols, phenol, amines, thioalcohols, and even polystyrene were achieved. The acylation of arenes was monitored by 31 P nuclear magnetic resonance and disclosed the existence of an acylphosphonium intermediate. The electrophilic capability of the acylphosphonium salt was ranked by the following series of controlled reactions: AcPR + ≈ AcOTf > AcI > AcCl.