Extended Data Fig. 1: ¹³C NMR spectrum of PTBL produced by ^tBu-P₄/Ph₂CHOH.

¹³C NMR spectrum (CDCl₃) of PTBL produced by ^tBu-P₄/Ph₂CHOH (Table 1, run 6). The observation of chemical resonances at 198.04 (>C = O) and 27.88 (–S–CH₂–) ppm clearly demonstrated the occurrence of IROP to form PTBL.