ESI‐FTICRMS Characterization of the Intermediates in Cycloisomerization of Trifluoromethyl‐substituted Enynols through Changing the Protecting Group of Substrate

Abstract

AbstractA chemical method of changing the protecting group was coupled to MS, deuterium‐labeled and NMR methods to characterize the intermediates in the palladium(II)‐catalyzed cycloisomerization of trifluoromethyl‐substituted enynols. It was demonstrated that the method of changing the protecting group of substrates not only caused a decrease in reaction speed, but also provided long‐lived reaction intermediates detectable by conventional spectroscopic techniques. In this sense, two assumed reaction intermediates were intercepted and detected by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS). For further characterization of these intermediates, the gas‐phase behavior of these intermediates was studied by sustained off‐resonance irradiation collision‐activated dissociation (SORI‐CAD) experiments. On the basis of the detailed, spectral interpretation of the palladium‐containing species, the fragmentation pathways of the intermediates have been proposed. The deuterium‐labeled experiment helped confirm the nature of the intermediates.