Lithiations of 1-trialkylsilylpyrroles: N to C silyl group rearrangement

Abstract

The sites of metallation with alkyl-lithium reagents of 1-trimethylsilyl- and 1-triethylsilyl-pyrroles have been explored under a variety of conditions. With short reaction times, BuⁿLi reacts with 1-trimethylsilylpyrrole in hexane predominantly at the 2-position though with Bu^tLi in pentane the unusual 3-metallated product is preferred. During prolonged reaction of 1-trimethylsilyl- and 1-triethylsilyl-pyrroles with Bu^tLi, the 2-monolithio- and the 2,4- and 2,5-dilithio-intermediates are formed, in which, unexpectedly, the silyl groups migrate to the pyrrole 2-position. Under conditions favouring enhanced ionicity, BuⁿLi cleaves the N–SiMe₃ bond in preference to ring metallation.