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Enantioselective photochemistry through Lewis acid-catalyzed triplet energy transfer.

ABSTRACT: Relatively few catalytic systems are able to control the stereochemistry of electronically excited organic intermediates. Here we report the discovery that a chiral Lewis acid complex can catalyze triplet energy transfer from an electronically excited photosensitizer. We applied this strategy to asymmetric [2 + 2] photocycloadditions of 2'-hydroxychalcones, using tris(bipyridyl) ruthenium(II) as a sensitizer. A variety of electrochemical, computational, and spectroscopic data rule out substrate activation by means of photoinduced electron transfer and instead support a mechanism in which Lewis acid coordination dramatically lowers the triplet energy of the chalcone substrate. We expect that this approach will enable chemists to more broadly apply their detailed understanding of chiral Lewis acid catalysis to stereocontrol in reactions involving electronically excited states.

SUBMITTER: Blum TR

PROVIDER: S-EPMC5501084 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature

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Enantioselective photochemistry through Lewis acid-catalyzed triplet energy transfer.

Blum Travis R TR Miller Zachary D ZD Bates Desiree M DM Guzei Ilia A IA Yoon Tehshik P TP

Science (New York, N.Y.) 20161201 6318

Relatively few catalytic systems are able to control the stereochemistry of electronically excited organic intermediates. Here we report the discovery that a chiral Lewis acid complex can catalyze triplet energy transfer from an electronically excited photosensitizer. We applied this strategy to asymmetric [2 + 2] photocycloadditions of 2'-hydroxychalcones, using tris(bipyridyl) ruthenium(II) as a sensitizer. A variety of electrochemical, computational, and spectroscopic data rule out substrate ...[more]

PMID: 27980203

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