Stereoselective routes to fichtelite (18-norabietane, la) and its C-4 epimer (19-norabietane, lb) from abietic acid via abietan-lhic acid (IC) are described. The latter acid on conversion into l% nor4 (18)-abietene (3) followed by hydrogenation or hydroboration and reduction yields principally fichtelite, whereas oxidation of the hydroboration product to 18-norabietan- 19-al (lh) followed by epimerization and reduction affords 19-norabietane. Similar ...
