First examples of Friedel–Crafts alkylation using ketals as alkylating agents: an expeditious access to the benzene-fused 8-oxabicyclo[3.2.1]octane ring system

Abstract

A novel acid-catalyzed intramolecular Friedel–Crafts alkylation (cyclization) using a spiroketal as electrophile leading to the otherwise not easily accessible benzene-fused 8-oxabicyclo[3.2.1]octane ring system in synthetically useful yields is reported. Slightly more than one equivalent of BF₃·OEt₂ in THF at refluxing temperature are found to be the most satisfactory conditions to achieve the desired cyclization. An electron-donating group para to the position where cyclization will take place greatly facilitates the reaction.