Catalytic C-Alkylation of Pyrroles with Primary Alcohols: Hans Fischer's Alkali and a New Method with Iridium P,N,P-Pincer Complexes

Hydrogen-autotransfer alkylation (HAT or “borrowing-hydrogen” alkylation) of heteroaromatic compounds has been studied with a range of substrates recently, but pyrroles have been largely absent from such studies. The conditions for HAT alkylations of pyrroles were investigated under a variety of conditions and were found to take place under basic alcoholic conditions (Hans Fischer alkylation) in the absence of transition-metal catalysts; by means of a heterogeneous Pd/C catalyst in the presence of base; and finally by means of homogeneous transition-metal catalysis combining a base and iridium pincer complexes generated in situ that have not previously been used in HAT alkylations of heterocycles.