title: Morita-Baylis-Hillman reaction: ESI-MS(/MS) investigation with charge tags and ionic liquid effect origin revealed by DFT calculations.
abstract: The use of a charge-tagged acrylate derivative bearing an imidazolium tag to study the Morita-Baylis-Hillman reaction via ESI-MS(/MS) monitoring and the effect of such tag (imidazolium cations and ion pairs) over TSs is described. The ionic nature of the substrate was meant to facilitate ESI transfer to the gas phase for direct mass spectrometric analysis. The detection and characterization of charged intermediates has suggested major reaction pathways. DFT calculations considering the effect of a polar and protic solvent (methanol), of a polar and aprotic solvent (acetonitrile), and of no solvent (gas phase) were used to predict possible TSs through a common accepted intermediate. The controversial proton transfer step, which may proceed via Aggarwal's or McQuade's proposals, was evaluated. Calculations predicted the formation of electrostatic intermediate complexes with both the cation and anion when charge-tagged reagents are used. These complexes contribute to the positive ionic liquid effect, and based on the formation of these unique complexes, a rationale for the ionic liquid effect is proposed. These complexes also pointed to a plausible explanation for the positive ionic liquid effect observed in several reactions that are difficult to be carried out in organic solvents but have shown a beneficial effect when performed in ionic liquids.
authors.affiliation: Laboratory of Medicinal and Technological Chemistry, University of Brasília, Chemistry Institute (IQ-UnB), Campus Universitário Darcy Ribeiro , P.O. Box 4478, 70904-970 Brasília, DF, Brazil.
authors.forename: Thyago S
authors.initials: TS
authors.lastname: Rodrigues
authors.forename: Valter H C
authors.initials: VH
authors.lastname: Silva
authors.forename: Priscila M
authors.initials: PM
authors.lastname: Lalli
authors.forename: Heibbe C B
authors.initials: HC
authors.lastname: de Oliveira
authors.forename: Wender A
authors.initials: WA
authors.lastname: da Silva
authors.forename: Fernando
authors.initials: F
authors.lastname: Coelho
authors.forename: Marcos N
authors.initials: MN
authors.lastname: Eberlin
authors.forename: Brenno A D
authors.initials: BA
authors.lastname: Neto
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D000179:Acrylates; D002384:Catalysis; D007093:Imidazoles / Q000737:chemistry*; D007202:Indicators and Reagents / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D011522:Protons; D012997:Solvents / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
chemical_list: D000097:Acetonitriles; D000179:Acrylates; D007093:Imidazoles; D007202:Indicators and Reagents; D052578:Ionic Liquids; D011522:Protons; D012997:Solvents; C036658:acrylic acid