Facile One-Pot Coupling−Aminovinylation Approach to Push−Pull Chromophores:  Alkyne Activation by Sonogashira Coupling

A straightforward coupling−aminovinylation sequence of terminal alkynes 1, electron-deficient heteroaryl halides 2, and secondary amines 4 furnishes highly solvochromic push−pull chromophores 5 in good yields. Semiempirical calculations (PM3) suggest that the aminovinylation proceeds in a stepwise fashion through a zwitterionic intermediate with a final rate-determining intramolecular protonation. Crucial parameters for the success of the amine addition are the relative LUMO energies and the charge distribution at the β-alkynyl carbon atom.