Two catalytic processes namely, palladium catalysis and Brønsted acid catalysis, lead to different alkylation products in the addition of alkoxyallenes to pyrazolones. In their Communication on
page 1077, G. Jiang et al. demonstrate how Pd catalysis provides branched allylic pyrazol-5-ones under mild conditions, whereas a chiral Brønsted acid catalyst gives the linear addition products.