Aluminum Chloride–Tetraalkylammonium Halide Complex as a Novel Catalyst in Friedel–Crafts Alkylation. Direct Construction of the Chroman Structure from 1,3-Diene

Abstract

Abstract Tetrabutylammonium halides were found to accelerate Lewis acid-catalyzed Friedel–Crafts alkylation when trimethylhydroquinone and myrcene were used, followed by cyclization to give the chroman compound predominantly. For tetraalkylammonium salts which have long-chain alkyls and/or bromide, iodide counter anions promote the reaction in less-polar solvents. Phosphonium halides and sulfonium halide were also effective. The tetraoctylammonium bromide–aluminum chloride complex was an effective catalyst for the initial regioselective protonation of 7,11,15-trimethyl-3-methylene-1,6-hexadecadiene to give α-tocopherol in high yield.