Abstract
In addition to the 2E, 6E- and 2Z,6E-hedycaryols (1 and 2) reported previously, we have synthesized the remaining two (2E,6Z- and 2Z,6Z-) isomers (3 and 4) by the anion-induced cyclization of 2E,6Z-10,11-epoxyfarnesyl phenyl thioether and the subsequent desulfurization. Their structures were based on the spectra and chemical correlations. Transannular reactions (acid-catalyzed cyclization and Cope rearrangement) of all four isomeric hedycaryols were investigated in order to clarify the stereochemistry of the reactions. From the stereochemistry of the products from the acid-catalyzed cyclization (eudesmol or dihydrooccidentalol) and from Cope rearrangement at lower temperature (≤400°), the conformers with the lowest activation energy were deduced for each isomer (Chart, p.5). Both reactions occur from the same conformation for each isomer. When the Cope rearrangement was carried out at a higher temperature (〜500°), more complicated reactions took place (Table, p.6), disclosing the occurrence of the Cope rearrangement from less favorable conformers of original hedycaryol and that from the initially-formed elemol to another hedycaryol. The structure of "epielemol" isolated by Pentegova from Pinus sibirica was revised to 26.
