Direct oxidative cyclization of 3-arylpropionic acids using PIFA or Oxone: synthesis of 3,4-dihydrocoumarins

The direct oxidative cyclization of 3-arylpropionic acids using PIFA or Oxone is reported. In the presence of BF3·OEt2, the reaction of 3-arylpropionic acids with PIFA or Oxone proceeded smoothly at 30 °C to give 3,4-dihydrocoumarins in good to excellent yields.