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 viaa 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 ,-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.