A ligand-free copper(II)-catalyzed three-component reaction in poly(ethylene glycol) medium: a versatile protocol for the preparation of selected 3-indole derivatives
A novel and ligand-free method was developed for the decarboxylative cross-coupling of alkynylcarboxylic acids with arylboronic acids. By using an environmentally friendly H2O–poly(ethylene glycol) (PEG-400) system as the reaction medium, a series of internal alkynes were synthesized in good yields and with remarkable selectivity. The Pd(OAc)2–H2O–PEG-400 catalytic system could be used for up to three cycles without any loss of activity, demonstrating the robustness of the approach.
