Azophilic Addition of Alkyllithium Reagents to Fluorenimines. The Synthesis of Secondary Amines

Article abstract of DOI:10.1021/jo00270a034

N-Alkyl- and N-arylfluorenimines undergo azophilic addition with n-BuLi to give N-butyl-N-alkyl- or N-butyl-N-aryl-9-aminofluorene systems.The fluorenyl group can then be hydrogenolyzed, furnishing the secondary amine.The selectivity for azophilic (vs carbophilic) addition ranges from 80 to 100percent for the N-alkylfluorenimines to 24-29percent for the N-arylfluorenimines.The decreased azophilic selectivity of the N-arylfluorenimines can be rationalized on the basis of frontier molecular orbital interactions as well as steric effects.Other related imines, that would appear toprovide an inverse polarization similar to that of the fluorenimines, do not give satisfactory yields of azophilic addition products.