Skip to content

Praziquantel: spot the fabricated intermediate

Single question

Three-step route to praziquantel: Pictet-Spengler to build the tetrahydroisoquinoline, then amide couple the cyclohexanecarboxylic acid, then couple piperazine. Look hard at the cyclized intermediate after the Pictet-Spengler.

Pictet-Spengler closes onto the arene, not onto a tethered carbamate oxygen
Mechanistic plausibility check on intermediates
Tetrahydroisoquinoline synthesis logic

Find the flaw

Click the step that contains the flaw, or pick “No flaw” if you think every step is correct.