Lead tetraacetate mediated one-pot multistage transformations: Theoretical studies on the diverging behavior in the Hajos-Parrish and Wieland-Miescher series


Unaleroglu C. , Aviyente V., Arseniyadis S.

JOURNAL OF ORGANIC CHEMISTRY, cilt.67, ss.2447-2452, 2002 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 67 Konu: 8
  • Basım Tarihi: 2002
  • Doi Numarası: 10.1021/jo0108481
  • Dergi Adı: JOURNAL OF ORGANIC CHEMISTRY
  • Sayfa Sayıları: ss.2447-2452

Özet

A computational approach to the proposed mechanistic rationale of the lead tetraacetate mediated oxidative cleavage of selected unsaturated diols in the hydrindenediol (derived from the Hajos-Parrish ketone, abbreviated as HP) and octalindiol (derived from the Wieland-Miescher ketone, abbreviated as WM) series is presented. These two unexpected cascade-type transformations have been found to yield structurally different products despite the similarities in the starting compounds 1-HP and 1-WM, which differ only by the number of carbon atoms in the cycloalkane rings, The final product in the HP series is the complex ring-expanded molecule iii-6, while the final product in the WM series is the ring-expanded bisacetoxy diacetal 7. Calculations carried out at the B3LYP/6-31G* level have revealed the fact that the transformations of i-6 to ii-6 and of i-7 to ii-7 are endothermic by 19.93 and 4.20 kcal/mol, respectively. The isomerization of compounds i to ii is more endothermic in the case of the HP series. Furthermore, calculations have shown the transformation of i to ii to be kinetically less favored in the HP series than in its analogue WM series. The activation barrier for the transformation of i-6 to ii-6 is calculated to be 22.09 kcal/mol, whereas the corresponding barrier in the WM series is 13.77 kcal/mol. The thermodynamic features of the reactions support the experimental findings as well: 7 is calculated to be more stable than iii-7, and iii-6 is more stable than 6, as expected. The diverging behavior in the mechanism of the interconversion of i to ii has been attributed to the stabilization of the positive charge by a carbonyl oxygen in ii-7 due to the flexibility of the seven-membered ring in contrast to the rigidity of the six-membered ring.