An important advantage of solid catalysts is recyclability. To screen the recyclability of the Amberlyst 15, two reactivation processes were applied to the material after catalysing reaction between 1 and 2a at in our reaction conditions (see Fig. ). While reuse of the catalyst after simple washing with an organic solvent (CH2Cl2) led to decreased activity in subsequent reactions, an addition wash with dilute hydrochloric acid maintained the efficiency of the catalyst for at least three subsequent reactions (likely due to the presence of organic material on the surface, which is eliminated after acid treatment).