Reactions of hydroxymethyl-substituted tetrathiatriarylmethanol with different acids are described. The reaction conditions were optimized for the selective synthesis of hydroxymethyl, methyl and aldehyde derivatives of trityl radicals as well as their deuterated analogues, which exhibit distinct EPR spectra and redox properties, thus suggesting applicability to in-cell EPR/dynamic nuclear polarization (DNP).

Abstract

Tetrathiatriarylmethyl radicals have found wide applications in electron paramagnetic resonance (EPR) spectroscopy and imaging as well as dynamic nuclear polarization (DNP). Recently, intense effort has been devoted to the derivatization of trityl radicals, but there is still a lack of highly efficient methods for access to these radicals. Herein, we report novel acid-mediated protocols for straightforward and selective synthesis of the hydroxymethyl, aldehyde and methyl derivatives of trityl radicals from the sole substrate hydroxymethyl-substituted tetrathiatriarylmethanol. The resulting trityl radicals exhibit various redox properties as shown by their cyclic voltammetric results. Importantly, the use of these protocols enables site-specific deuteration of the three trityl radicals, which show unique EPR spectral properties. Overall, our study reveals the crucial effect of the acids on the synthesis of these trityl radicals and provides a new approach for selective access to different trityl radicals, thus enriching their synthetic chemistry.