A Ring Cyclized Product from the Delepine Reaction

As part of our studies towards the synthesis of 4-hydroxy-1,2,3,4-tetrahydroisoquinoline derivatives with oxygen functions at C-6 and C-8, we required 6,8-dibenzyloxy-4-oxo-1,2,3,4-tetrahydroisoquinolinium chloride (II). We report here that the standard Delepine reaction conditions 1 may be used to convert an appropriately substituted phenacyl bromide into the 4-oxo-tetrahydroisoquinoline derivative. A convenient synthesis is not obtainable through Dieckmann condensation 2 due to inaccessibility of starting material nor through N -benzyl-glycines 3 nor substituted nitriles 4 due to lack of activation by oxygenation at C-7.