Journal
SCIENCE
Volume 342, Issue 6160, Pages 840-843Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1244809
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Funding
- Deutsche Forschungsgemeinschaft (Graduiertenkolleg GRK 1626 Chemical Photocatalysis)
- Fonds der Chemischen Industrie
- Division Of Ocean Sciences
- Directorate For Geosciences [1636445] Funding Source: National Science Foundation
- Division Of Ocean Sciences
- Directorate For Geosciences [1203892] Funding Source: National Science Foundation
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Asymmetric catalysis of photochemical cycloadditions has been limited by the challenge of suppressing the unselective background reaction. Here, we report that the high cross-section pi pi* transition of 5,6-dihydro-4-pyridones, a versatile class of enone substrates, undergoes a >50 nanometer (nm) bathochromic absorption shift upon Lewis acid coordination. Based on this observation, enantioselective intramolecular [2+2] photocycloaddition reactions (82 to 90% enantiomeric excess) were achieved with these substrates using 0.5 equivalents of a chiral Lewis acid upon irradiation at a wavelength of 366 nm. One of the products was applied as a key intermediate in the total synthesis of (+)-lupinine and the formal synthesis of (+)-thermopsine. Several enones show similar bathochromic shifts in the presence of a Lewis acid, indicating that chiral Lewis acid catalysis may be a general approach toward enantioselective enone [2+2] photocycloadditions.
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