The intermolecular Pictet-Spengler condensation with chiral carbonyl derivatives in the stereoselective syntheses of optically-active isoquinoline and indole alkaloids

The stereoselective Pictet-Spengler synthesis is one of the currently most important synthetic methodologies for the preparation of polysubstituted optically active tetrahydroisoquinolines and tetrahydro-beta-carboline derivatives functionalized on C-1. The intermolecular Pictet-Spengler condensation with chiral carbonyl derivatives constitutes an interesting and useful approach towards this goal, as summarized in this review. Strategies covered, which were developed during the last 15 years, include the intermolecular Pictet-Spengler reaction with the use of carbonyl derivatives tethered to removable chiral auxiliaries and the cyclocondensation of beta-arylethylamines with chiral carbonyl components. Brief mention is also made to the occurrence of asymmetric beta-carbolines in foodstuffs.