General acid-catalyzed oxidative cyclization procedure B. The dipeptide (1 eq) was diluted in anhydrous DCM (0.02 M) and cooled to -78°C. N2 gas was bubbled into the solution for 5 minutes, followed by ozone (~80% output). When the solution turned a deep blue, ozone addition was immediately stopped, and N2 was bubbled until the solution was colorless. Polymer-bound triphenylphospine (1.5 eq, ~3mmol/g loading, CAS 39319-11-4) was added, and the mixture stirred for 5 minutes at -78°C, then at room temperature overnight, after which the mixture became slightly opaque. TFA (1.5 eq) was added at room temperature, and the mixture was stirred for 2h.