Efficient and suitable preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and ring analogues using recyclable H6P2W18O62·24H2O/SiO2 catalyst

Silica gel-supported H 6 P 2 W 18 O 62 ·24H 2 O 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 H 6 P 2 W 18 O 62 ·24H 2 O. Reactions were performed in a low volume of toluene, at 70 °C and for a short time, typically 15 to 30 min. 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.