The role of ionic liquids in co-catalysis of Baylis-Hillman reaction: Interception of supramolecular species via electrospray ionization mass spectrometry

The Baylis-Hillman reaction is a general and multifaceted method for C-C bond formation in organic synthesis. Using electrospray ionization mass spectrometry in both the positive and negative ion modes, we performed on-line monitoring of the reaction in the presence of imidazolium ionic liquids. Loosely bonded supramolecular species formed by coordination of neutral reagents, products and the protonated forms of zwitterionic Baylis-Hillman intermediates with cations and anions of ionic liquids were gently and efficiently transferred directly from the solution to the gas phase. Mass measurements and structural characterization of these unprecedented species via collision-induced dissociation in tandem mass spectrometry experiments were performed. The interception of several supramolecular species indicates that ionic liquids co-catalyze Baylis-Hillman reactions by activating the aldehyde toward nucleophilic enolate attack and by stabilizing the zwitterionic species that act as the main BH intermediates. Copyright (c) 2006 John Wiley & Sons, Ltd.