Abstract Spectra and chemical transformations allow to establish the gross structure 6, 7- epoxy-4, 7-dimethyl-l-oxa-spiro [4.4] non-3-en-2-one for adriadysiolide (1), the first monoterpenoid isolated from a marine sponge, a Dysidea sp. of the Adriatic Sea. Its configuration 5R*, 6S*, 7S* as given in 1a is derived from diastereoselective total syntheses of both 1a and its diastereoisomer 1bvia stereochemically predictable peracid ...
