An umpolung of Lewis acidity/basicity at nitrogen by deprotonation of a cyclic (amino)(aryl)nitrenium cation

Abstract

A cyclic (amino)(aryl)nitrenium cation 2 has been achieved by treatment of spiro[fluorene-9,3′-indazole] (1) with Ph₂CHCl and AgBF₄. This cation 2 is Lewis acidic at nitrenium N1, reacting with PMe₃ affording a Lewis acid/base adduct 3. In contrast, deprotonation of 2 with other bases provides a neutral compound 4 which is Lewis basic at N1, reacting with electrophiles including GaCl₃, MeOTf and PhNCO.