The degree of hydrolysis of polyphosphoric acid (PPA) has a crucial effect on the regioselectivity of the PPA-mediated synthesis of indanones. It was found that the regioselectivity can be switched by employing PPA with either a high or low content of P2O5. This methodology was used for the regioselective synthesis of a range of electron-rich indanones, including a natural sesquiterpene.
MERCHANT J.R.; KAMATH M.S.; DIKE S.Y., J. CHEM. SOC. PERKIN TRANS. 1977, PART 1 NO 19, 1977