Co-Authors:
Hart, H., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Dunkelblum, E., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Abstract:
Irradiation of the three isomeric benzocycloheptadienones 10, 14, and 15 produces in each case a trans intermediate which can be trapped by furan. In the absence of a trapping agent, cyclobutane dimers are formed whose stereochemistry, established mainly by X-ray diffraction on crystals, differs for each of the three substrates (10 → 12; 14 → 18, 19; 15 → 22, 23, 24, 25). The formation of head-to-tail dimers 23 and 25 is novel and argues against a diradical mechanism. Dimer stereochemistry corresponds to a π;2 s + π2 a ground state cycloaddition between two trans species for 10, a trans + cis species for 14, and both types for 15. A rationale in terms of the most strained trans intermediate being the least selective for its reaction partner is proposed to explain the results. © 1979 American Chemical Society.
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