Transition-Metal-Free Terminal Alkyne Addition to Isatins

Abstract

A ‘direct’ alkynylation of isatins, which uses potassium <i>tert</i>-butoxide to provide the desired 3-hydroxy-3-ethynyl-2-oxindoles in good to high yields, is reported. This protocol proceeds smoothly for both electron-rich and electron-deficient alkynes in comparable reaction rates and does not require any specially design ligand or expensive transition-metal catalysts.