Silica gel-supported H₆P₂W₁₈O₆₂·24H₂O is an efficient and recyclable catalyst for the synthesis of biologically important molecules. Several substituted N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and ring analogues can be prepared in very good yields and purity by direct reaction of N-aralkylsulfonamides and sym-trioxane by a Pictet-Spengler reaction in the presence of a catalytic amount of silica gel-supported H₆P₂W₁₈O₆₂·24H₂O. Reactions were performed in a low volume of toluene, at 70°C and for a short time, typically 15 to 30min. The title heterocyclic compounds were prepared in very good yields (60%–95%) using the described procedure results in a clean and useful alternative, which has the advantages of a greener methodology with operative simplicity, use of a reusable and non-corrosive solid catalyst, soft reaction conditions, low reaction times, and good yields.