STEREOCHEMISTRY OF ALLYLIC REARRANGEMENTS .17. ACID-CATALYZED REARRANGEMENT OF EXO AND ENDO-BICYCLO[3.2.1]OCT-3-EN-2-OL

The acid-catalyzed rearrangement of exo-and endo-bicyclo[3.2.1]oct-3-en-2-ol (2-OH) in 33.3% aqueous acetone results in interconversion of enantiomers (racemization) and exo ↔ endo isomerization. Rate constants have been determined for (1) loss of optical activity (kα), (2) exo ↔ endo equilibration (Keq) and 18O exchange (kexo) for both isomers. Reactivity ratios (Kα-exo/Kαk-endo range from 247 at 20 °C to 136 at 49 °C. The partition ratio for solvent capture of the symmetrical bicyclo[3.2.1]oct-3-en-2-yl cation (3) ranges from 878 at 20 °C to 454 at 49 °C (exo capture favored). The activation energy difference for exo and endo capture (AEa) is 4.4 ± 0.5 kcal mol-1 and AH for the exo endo equilibration is 0.6 ° 0.2 kcal mol-1(exo isomer more stable). The Kexo/Kα ratio is 0.67 for exo-2-OH and 1 for endo-2-OH. © 1979, American Chemical Society. All rights reserved.