Total Synthesis of Alanense A through an Intramolecular Friedel–Crafts Alkylation

The first total synthesis of cadinane sesquiterpenoid alanense A, in which an intramolecular dehydrative Friedel–Crafts alkylation of 2,5-diaryl-2-pentanol is incorporated as a key step, has been achieved. The combinatorial use of p-TsOH·H₂O as a catalyst and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a solvent provides 1,1-disubstituted tetrahydronaphthalene in 97% yield. It was also found that the combination of p-TsOH and HFIP is effective for the removal of phenolic MOM ether.