Practical Large-Scale Regioselective Zincation of Chromone Using TMPZnCl·LiCl Triggered by the Presence or Absence of MgCl₂

Abstract

Chromones are efficiently zincated in position C(3) in THF by using the commercially available amide base TMPZnCl·LiCl (TMP = 2,2,6,6-tetramethylpiperidyl). Additionally, in the presence of a Lewis acid such as MgCl2, zincation using TMPZnCl·LiCl occurs at C(2). These metalation reactions are carried out on a 50 mmol scale, and the metalation selectivities have been compared with the corresponding small-scale reactions (2 mmol). The resulting zinc organometallics undergo smooth reactions with various electrophiles, for example, Pd-catalyzed cross-coupling reactions or Cu-catalyzed acylations or allylations.