New in situ trapping metalations of functionalized arenes and heteroarenes with TMPLi in the presence of ZnCl2 and other metal salts

Abstract

The addition of TMPLi to a mixture of an aromatic or heteroaromatic substrate with a metal salt such as MgCl2, ZnCl2, or CuCN at -78 °C first leads to lithiation of the arene followed by transmetalation with the metal salt to afford functionalized organometallic compounds of Mg, Zn, or Cu. This in situ trapping method allows an expedited metalation (-78 °C, 5 min) of a range of sensitive pyridines (bearing a nitro, ester, or cyano group) and allows the preparation of kinetic regioisomers of functionalized aromatic compounds or heterocycles not otherwise available by standard metalating agents, such as TMPMgCl·LiCl or TMPZnCl·LiCl. Fast, faster, the fastest: Aromatic and heterocyclic substrates, when treated with TMPLi (TMP=2,2,6,6-tetramethylpiperidyl), undergo a kinetic lithiation and then a transmetalation with a metal salt such as MgCl2, ZnCl 2, or CuCN. This allows an expedited metalation of sensitive pyridines bearing a nitro, ester, or cyano group and allows the preparation of kinetic regioisomers of functionalized aromatic compounds or heterocycles. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.