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The racemic form of the metabolite of the Dysidea sea sponge, furanoterpenoid pallescensin A, was synthesized by cationic cyclization of the sulfonyl-substituted linear sesquiterpene precursor.Key words: furanoterpenoid, pallescensin A; derivative of farnesol, cationic cyclization.Previously, ! we have attempted to synthesize the racemic form of the metabolite of the Dysidea sea sponge,-" pallescensin A (1). We planned to prepare the key intermediate needed for this synthesis, viz., appropriately functionalized octaline 2, by the cationic cyclization (CC) of the available linear sesquiterpene alcohol 3. However, realization of this scheme was hampered by an unfavorable regio-and stereochemical outcome of +Deceased.the CC of triene 3; even under the optimal conditions, this reaction gave a mixture of products 5 in which undesirable regioisomers (regarding the position of the multiple bond) 5a,b predominated (Scheme l). Moreover, the minor component of the resulting mixture 5c, whose primary structure was suitable for the subsequent building of the furan fragment of molecule l, was built, unlike the latter, from cis-fused rings A and B.In view of the known 3 fact that an c~-phenylsulfonyl group promotes the stabilization of type 9 carbocation to give mostly a sulfone of the atlylic series, in the present work, we studied the possibility of controlling the regioselectivity of the key step in the scheme chosen for the synthesis of furanoterpenoid 1 using the appropriately functionalized trienol 4 as the substrate for CC. This compound was prepared by alkylation of the dilithium derivative 14 of hydroxysulfone 134 with geranyt bromide 12.The cationic cyclization of triene 4 was carried out using a ~6.5-fold excess of HSO3F in 2-nitropropane at -80 ~ The reaction yielded a complex mixture of

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