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Updated: Jun 28, 2026
Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
Published on: November 29, 2018
Stereoretentive Norrish-Yang Photocyclization Mediated by Hydrogen Bonding
Enrico Sfreddo1, Aleksa Durdevic1, Andrea Palone1
1University of Bologna, Department of Industrial Chemistry Toso Montanari, via Piero Gobetti 85, 40129 Bologna, Italy.
Abstract:
The Norrish-Yang photocyclization of aryl alkyl ketones is a classical photochemical transformation that proceeds through triplet 1,4-diradicals whose conformations govern the fate of the reaction. Directing the reactivity of these diradicals is difficult because they can evolve through competing pathways, including cyclization and Norrish type II fragmentation. Achieving stereocontrol is even more challenging because radicals generated from enantiopure substrates are expected to undergo rapid configurational scrambling. Here we report a stereoretentive Norrish-Yang photocyclization of enantiopure aryl alkyl ketones enabled by hydrogen-bond-guided conformational control of the photogenerated 1,4-diradical. Hydrogen-bonding units encoded within the chiral substrate bias the reactive diradical manifold toward cyclization while suppressing fragmentation and stereochemical erosion. The reaction affords highly enantioenriched spirocyclobutanol-containing amines and related cyclobutanols bearing two stereocenters, with high enantiospecificity across a range of amino-acid-derived substrates.
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