Intermolecular transposed Paternò-Büchi reactions enabled by triplet sensitization
Tahoe A Fiala1, Omar A Solis1, Jesse B Kidd1
1Department of Chemistry, University of Wisconsin-Madison 1101 University Avenue Madison WI 53706 USA tyoon@chem.wisc.edu.
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The canonical mechanism of the Paternò-Büchi cycloaddition involves the reaction of an excited-state carbonyl compound with a ground-state alkene to afford an oxetane. Despite a century of sustained interest in this important organic photoreaction, the mechanistically complementary reaction proceeding via an excited-state alkene and ground-state carbonyl compound was first reported less than a decade ago and remains relatively underdeveloped. We report herein a visible light induced photocatalytic approach towards transposed Paternò-Büchi cycloadditions. This strategy involves the use of a photosensitizer that is capable of engaging in selective triplet energy transfer to the alkene component in preference to its carbonyl reaction partner. These more general reaction conditions have enabled a thorough investigation of the synthetic opportunities afforded by the transposed Paternò-Büchi reaction.
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