Catalytic enantioselective 6𝝿 photocyclization of acrylanilides



Controlling absolute stereochemistry in catalytic photochemical reactions is generally challenging owing to high rates of background reactivity. Successful strategies broadly rely on selective excitation of the reaction substrate when associated with a chiral catalyst. Recent stud-ies have demonstrated that chiral Lewis acid complexes can enable selective energy transfer from a photosensitizer to facilitate enantiose-lective triplet state reactions. Here, we apply this approach to the enantioselective catalysis of a 6π photocyclization through the design of an iridium photosensitizer optimized to undergo energy transfer to a reaction substrate only in the presence of a chiral Lewis acid complex. Amongst a group of iridium(III) sensitizers, enantioselectivity and yield closely correlate with photocatalyst triplet energy within a narrow window enabled by a modest reduction in substrate triplet energy upon binding a scandium/ligand complex. These results demonstrate that photocatalyst tuning offers a means to suppress background reactivity and improve enantioselectivity in photochemical reactions.


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Supporting Information
All data (experimental procedures, characterization data, computational data) supporting the findings of this study are available within the article and its supporting information. Crystallographic data for compounds 5 and 17 has been deposited with the Cambridge Crystal-lographic Data Centre under deposition number (CCDC 2192819 and 2192820 respectively).