N-Aminomethylation vs. C-Aminomethylation of Indole and Pyrrole with an N,O-Acetal Controlled by the Hardness of a Counter Ion of an Iminium Compound.

Under relatively strong Lewis acidic conditions (a softer counter ion) using TMSOTf and TMSI, the aminomethylation of indole or pyrrole with a typical N,O-acetal preferentially produced the kinetically favored N-aminomethylated indole or pyrrole derivative. Use of a relatively weak Lewis acid (a harder counter ion), such as TMSCl and TMSBr, preferentially produced the thermodynamically favored C-aminomethylated indole and pyrrole derivative. [ABSTRACT FROM AUTHOR]