Abstract
A Novel Example of Reversible Ring Opening: The Epimerization at C(3) of Sugar 3‐Hydroxy‐Δ1‐pyrazolinesReaction of 1 (either geometrical isomer) with hydrazine followed by in situ Ag2O oxidation led to two pairs of interconverting isomers 4 ⇄ 5 and 6 ⇄ 7. By the same treatment, (Z)‐10 and (or) (E)‐10 gave the pair 11 ⇄ 12. Acetylation of 4 ⇄ 5 led to a non interconverting mixture of 8 and 9. This fact, and the lack of incorporation of 18O when the epimerization took place in the presence of H218O indicated that the most probable mechanism consisted in a reversible ring opening (D ⇄ E ⇄ F). The kinetic parameters of these reactions are given and structural assignments proposed for the new compounds.
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