Recognition motif for enantiodiscrimination generally maintained, the ratio of acylated heterocycle to ringopened ester was significantly affected (entries 5-14). For example, THF gave the highest proportion (25%) of ring-opened product (entry 5), while toluene gave the highest proportion of the desired product (93:7 ratio), giving 2 in 80% yield and 97:3 er (entry 8). In toluene, acetic and propionic anhydride gave reasonable product enantioselectivity but a 75:25 ratio of acylated heterocycle to ring-opened ester products, while 2,2diphenylacetic anhydride gave a 50:50 mixture of products, with 2 in reduced enantioselectivity (entry 12). Further optimization using toluene as the reaction solvent showed that decreasing the catalyst loading and anhydride stoichiometry was possible alongside further simplification of the reaction conditions through the removal of base (entries 13-15). Using 5 mol% of HyperBTM (entry 14) was considered optimal, giving 2 in 80% isolated yield and 97:3 er.