The benzoin condensation: Charge tagging of the catalyst allows for tracking by mass spectrometry

A novel thiazolium with a sulfonate charge tag was synthesized to test the feasibility of tracking the progress of a thiazolylidene-catalyzed benzoin condensation reaction using electrospray ionization-mass spectrometry (ESI-MS). Intermediates in the benzoin condensation were fished out of a reaction mixture and detected using MS. Tandem MS and calculations were used to support structural assignments. The results are consistent with the Breslow mechanism. These data show the viability of synthesizing negatively charged compounds that will both catalyze and track reactions involving N-heterocyclic carbene organocatalysis, which are becoming increasingly prevalent in organic synthesis. (C) 2014 Elsevier B.V. All rights reserved.