α-Halogenoacetanilides as hydrogen-bonding organocatalysts that activate carbonyl bonds: fluorine versus chlorine and bromine.

-Halogenoacetanilides (X=F, Cl, Br) were examined as H-bonding organocatalysts designed for the double activation of CO bonds through NH and CH donor groups. Depending on the halide substituents, the double H-bond involved a nonconventional CHO interaction with either a HCXn (n=1-2, X=Cl, Br) or a HCAr bond (X=F), as shown in the solid-state crystal structures and by molecular modeling. In addition, the catalytic properties of -halogenoacetanilides were evaluated in the ring-opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst. The -dichloro- and -dibromoacetanilides containing electron-deficient aromatic groups afforded the most attractive double H-bonding properties towards CO bonds, with a NHOHCX2 interaction.