Figure 6

(A) The HPLC spectra of 1a at different intervals in methanol; (B) The HPLC spectra of 1b at different intervals in methanol; (C) The conversion curve of 1a to 1b in methanol; (D) The conversion curve of 1b to 1a in methanol; (E) The HPLC spectra of 2a at different intervals in methanol; (F) The HPLC spectra of 2b at different intervals in methanol; (G) The conversion curve of 2a to 2b in methanol; (H) The conversion curve of 2b to 2a in methanol.