Copper-catalyzed direct thiolation of xanthines and related heterocycles with disulfides

A novel copper-catalyzed, base-free direct thiolation of xanthines and related heterocycles is described, featuring the use of inexpensive Cu(OAc)2·H2O as the catalyst, O2 as a clean and cheap oxidant, and easy-to-handle disulfides as the thiolation reagents. It works well for both aryl and alkyl disulfides. Moreover, the resultant products can be converted into 8-(hetero)aryl- or alkenyl-substituted xanthines in good yields via the Liebeskind-Srogl coupling reaction.