Trifluoromethanesulfonic acid mediated Friedel–Crafts reaction of (E)-3-aryl-2-(diethoxyphosphoryl)acrylic acids with electron-rich hydroxyarenes. A convenient approach to α-methylene-δ-valerolactones

The synthesis of trans-3-diethoxyphosphoryl-4-aryl-3,4-dihydrocoumarins from electron-rich hydroxyarenes and (E)-3-aryl-2-(diethoxyphosphoryl)acrylic acids has been achieved by using CF3SO3H as a catalyst. The products could be easily transformed to the corresponding α-methylene-δ-valerolactones by means of the Horner–Wadsworth–Emmons reaction.