Journal
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
Volume 2012, Issue 6, Pages 1186-1194Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.201101301
Keywords
Cycloaddition; Density functional calculations; Diastereoselectivity; Steric hindrance
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Funding
- Natural Sciences and Engineering Research Council of Canada
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The facial selectivity in the DielsAlder reactions via endo transition states of the plane-nonsymmetric dienophiles spiro[bicyclo[2.2.2]octane-2,1'-[3]cyclopentene]-2',5'-dione (6) and spiro[bicyclo[2.2.1]heptane-2,1'-[3]cyclopentene]-2',5'-dione (7) has been found to be very similar to the facial selectivity of reactions of cyclopentadienes fused to bicyclo[2.2.2]octane and bicyclo[2.2.1]heptane (4 and 5). This is strong evidence for steric control in their facial selectivities. Density functional computations involving the reactions of these compounds, as well as a series of conformationally locked model addends (26ac and 27ac), revealed geometrical and energetic properties that confirmed that the facial selectivity is governed by steric effects. Steric interactions appeared to be the reason for the low endo/exo selectivity of dienophiles 6, 7, 2,2-dimethylcyclopent-4-ene-1,3-dione (20), and spiro[5.4]dec-8-ene-7,10-dione (23).
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