jo500799j_si_001.pdf (1.98 MB)
Morita–Baylis–Hillman Reaction: ESI-MS(/MS) Investigation with Charge Tags and Ionic Liquid Effect Origin Revealed by DFT Calculations
journal contribution
posted on 2014-06-06, 00:00 authored by Thyago
S. Rodrigues, Valter H. C. Silva, Priscila M. Lalli, Heibbe
C. B. de Oliveira, Wender A. da Silva, Fernando Coelho, Marcos N. Eberlin, Brenno A. D. NetoThe
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.