Diastereoselective construction of cis 2,6-disubstituted tetrahydropyran rings via In(OTf)3-catalyzed intramolecular 2,5-oxonium-ene cyclization:: synthetic studies towards the total synthesis of zampanolide and dactylolide

Diastereoselective construction of 2,6-disubstituted tetrahydropyrans with an exocyclic double bond was achieved via the In(OTf)(3)-catalyzed intramolecular 2,5-oxonium-ene cyclization. Its application was further demonstrated by the synthesis of a common intermediate for both zampanolide and dactylolide, fragment I, with a total yield of 42% in three steps starting from (2E)-3-bromobut-2-enal. (C) 2002 Elsevier Science Ltd. All rights reserved.