Mechanical Trapping of the Phlorin Intermediate

Trapping unstable intermediates for elucidating reaction mechanisms in chemistry presents a formidable challenge.There has long been a lack of direct evidence for key intermediates like the highly reactive phlorin leading to porphyrin.Here,we report a molecular-strain engineering(MSE)strategy that harnesses intramolecular strain to trap the native phlorin during porphyrin synthesis.By mechanically constraining its periphery,a phlorin stable towards oxidation was captured as an isolable intermediate and fully characterized.