First Continuous‐Flow Intramolecular Dehydrative Friedel–Crafts Alkylation of Benzyl Alcohols in 1,1,1,3,3,3‐Hexafluoro‐2‐Propanol Catalyzed by HO‐Substituted Sulfonic Acid‐Functionalized Silica Gel

The first continuous‐flow intramolecular dehydrative Friedel–Crafts alkylation of 1‐substituted ω‐arylalkan‐1‐ols is successfully achieved. The reaction is completed by a single pass of a solution of substrates in 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) at 25 °C through a cartridge packed with hydroxy‐substituted sulfonic acid‐functionalized silica gel (HO‐SAS) as a water‐tolerant immobilized Brønsted acid catalyst with a residence time of only 40–80 s. The efficiency of the concise catalytic process is demonstrated by the short‐step synthesis of the bisnorlignan natural product pachypostaudin A.