Electron spray ionization mass spectrometry ESI-MS

In 2010, Xia, Huang and co-workers reported an iron-assisted chiral phosphoric acid catalyst for the Fridel-Crafts reaction between indole and 3-aryl a -hydroxy enones (Fig. 16) [70]. Due to the evidence from electron spray ionization mass spectrometry (ESI-MS) analysis for the presence of iron phosphate salt, an iron/ proton dual activation mechanism was proposed to account the observed reactivity/ selectivity trends. Addition of a third acid component, silver triflate, was shown to be beneficial for the enantioselectivity, presumably by exchanging chloride to the less coordinating triflate anion. 

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