Stereoelectronic Effects in the Iodine‐Promoted Oxidation of Pentacyclic Tetrahydroisoquinolines

Iodine‐promoted oxidations of the pentacyclic tetrahydroisoquinolines 4a, 4b , and 10 were investigated. Whereas the all‐ cis diastereoisomer 4a containing an arylamino moiety gave the iminium ion 5 as the primary product, which subsequently underwent intramolecular aminal formation to 6 , the corresponding all‐ trans diastereoisomer 4b epimerized to the all‐ cis diastereoisomer 4a via iminium ion 7 . In contrast, tetrahydroisoquinoline 10 could be cleanly oxidized to the corresponding isoquinolizidinium ion 11 . Mechanistic considerations were supported by molecular‐modeling calculations.