Syntheses of exo- and endo-lsofenchor

Abstract

(+)-endo-Fenchol [1] was dehydrated with KHSO4 to give δ-, cyclo-, γ-, ε-, β-, and a-fenchenes ([2]-[8]). (+)-exo-Isofenchol [9] was obtained by the hydration of these fenchenes. (-)-endo-Isofenchol (11) was synthesized selectively by reduction with LiAlH4 of isofenchone [10] which in turn was obtained by oxidation of [9]. The structu res of [9] and [11] were confirmed by the NMR measurement of pseudocontact shift due to an added shift reagent.
The sample of [9] has elegant fragrance similar to nojigiku alcohol [A] or 6-exo-hydroxyexoisocamphane [B] whereas [11] has borneol-like odor.