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Dynamic solvation effects on the endo/exo selectivity of the Diels–Alder reaction

✍ Scribed by Gianfranco Cainelli; Paola Galletti; Daria Giacomini; Arianna Quintavalla

Publisher
Elsevier Science
Year
2003
Tongue
French
Weight
122 KB
Volume
44
Category
Article
ISSN
0040-4039

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✦ Synopsis

The endo/exo stereoselectivity of the Diels-Alder cycloaddition between cyclopentadiene and 3-crotonoyl-2-oxazolidinone catalysed by Et 2 AlCl is temperature-and solvent-dependent. Eyring plots of ln(endo/exo) versus 1/T show different inversion temperatures (T inv ) depending on the reaction solvent. Using toluene-d 8 we found a break temperature (T NMR ) in a variable temperature 13 C NMR experiment of the starting oxazolidinone, and this T NMR corresponded to the T inv . In several cases the differential activation entropy manages the observed stereoselectivity.

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We have recently determined kinetic parameters for the unimolecular Diels-Alder retrogressions of exe and w-dicyclopentadiene to monomer (1). The activation enthalpies and entropies are aH f (E) 37.4 2 0.3 kcal/mole, hSS (E) + 1.1 2 0.6 e.u., hH + (&) 33.0 2 0.5 kcal/mole, and hSS (endo) \_ -1.9 +