Preparation of 1-Substituted Tetrahydro-β-carbolines by Lithiation-Substitution.
A method to prepare 1-substituted N-Boc-tetrahydro-β-carbolines was developed by lithiation followed by electrophilic substitution. The deprotonation to give the organolithium was optimized by in situ IR spectroscopy and showed that the Boc group rotates slowly at low temperature. The chemistry was applied to the synthesis of 9-methyleleagnine (N-methyltetrahydroharman) and 11-methylharmicine.