Full conversion of 2a was achieved after 3 hours of irradiation and the bicyclic product 3a resulting from a 6-endo cyclization was obtained in 72% yield. The long reaction time necessary to reach full conversion was puzzling since the overall one-pot annulation process was complete within less than 20 minutes. Since acetic acid (one equivalent) is generated during the allylation step leading to 2a, the reaction was repeated in the presence of one equivalent of acetic acid. Remarkably, the cyclization was finished in 3 minutes and an improved yield of 91% was obtained. Running the reaction with CsOPiv (1.2 equiv) and acetic acid (1.0 equiv) afforded the cyclized product in nearly quantitative yield within 2 minutes. This is in accordance with findings reported by Yoon and co-workers where their photocatalytic addition of α-aminoalkyl radicals on Michael acceptors was improved by the addition of a Brønsted acids such as TFA. Scheme 4. Cyclization of the mono-allylated pyrrolidine 2a, influence of acid additive.