Iron(III) Chloride‐Catalyzed Tandem Aza‐Prins/Friedel–Crafts Cyclization of 2‐Arylethyl‐2,3‐butadienyl Tosylamides and Aldehydes‐An Efficient Synthesis of Benzo[f]isoquinolines

An efficient approach for the synthesis of 1,2,3,4,5,6‐hexahydrobenzo[f]isoquinolines via a tandem aza‐Prins/Friedel–Crafts cyclization from 2‐arylethyl‐2,3‐butadienyl tosylamides and aldehydes has been developed. This iron(III) chloride‐catalyzed cascade cyclization at the room temperature with different types of aldehydes, such as aromatic and heteroaromatic aldehydes, alkyl aldehydes, and α,β‐unsaturated aldehydes, affords the products in moderate to excellent yields (up to 97 %). In this reaction, chlorotrimethylsilane was applied to activate the aldehydes. The cheap catalyst, the mild reaction conditions, and the broad scope of the substrates make this method highly useful.