As discussed, the conversion of 2 to 5a involves a complex rearrangement reaction, and we were curious to determine if the reaction is influenced by a temperature change. To explore this possibility, reac ons were conducted across a temperature range of -10 to 25 ℃ using Cu(CF3COO)2 as the catalyst and LiOH as the base. The ideal temperature range was found to be within 17-18 ℃. A study of the reaction kinetics at this temperature revealed that the yield peaked at 1.5 h and subsequently decreased, owing to the degradation of the product (see Supplementary Information Fig. ). Finally, to study the molecular rearrangement mechanism involved in the formation of 5a, the ester carbonyl carbon atom in molecule 2 and its α-carbon atom were labelled with isotope C. Using the optimised reaction conditions described in this work, we obtained C-labelled 5a which was subsequently analysed via NMR (see Supplementary Information Figs. S14-S16). The mechanism for molecular rearrangement to produce 5a, based on NMR analysis, is shown in Fig. .