Pictet—Spengler Condensation of N-Sulfonyl-β-phenethylamines with α-Chloro-α-phenylselenoesters. New Synthesis of 1,2,3,4-Tetrahydroisoquinoline-1-carboxylates.

The reaction of N-sulfonyl-β-phenethylamines with α-chloro-α-phenylseleno acetate/propionate esters under Lewis acid promotion gives moderate to good yields of the corresponding 1,2,3,4-tetrahydroisoquinoline-1-carboxylates. Varying degrees of diastereoselection were obtained using chiral sulfonamides and/or esters. Employing this strategy, the achievement of a new total synthesis of Calycotomine is reported.