INFLUENCE OF CONFORMATIONAL FACTORS ON ACID-CATALYZED CYCLIZATIONS OFGERMACRANOLIDES - MOLECULAR-STRUCTURE OF THE CYCLIZATION PRODUCTS OF GALLICIN AND 8-ALPHA-HYDROXYGALLICIN (SHONACHALIN-A)

Acid-catalyzed cyclization of the natural germacranolide gallicin (8) yielded, among other products, the 1,4-epoxyeudesmanolide 9, which has a trans-fused decaline system. Under the same conditions the closely related germacranolide shonachalin A (8 alpha-hydroxygallicin) (3) cyc lized to the eudesmanolide 4 with a cis-fused decaline system. The str uctures of these cyclization products were secured by means of chemica l correlations and X-ray diffraction analyses.