General synthesis of persistent trityl radicals for EPR imaging of biological systems.

In this paper we describe the syntheses of the tetraoxygenated triarylmethyl (trityl) radical 14 and the tetrathiatriarylmethyl (trityl) radicals 15 and 16. The syntheses include new and improved preparations of the key intermediate compounds 1 and 2. The new route to compound 2 is noteworthy for its efficiency and its avoidance of the highly toxic compound phosgene as well as the isolation of the air-sensitive 1,2,4,5-benzenetetrathiol.