Diverse Reactions of Thiophenes, Selenophenes, and Tellurophenes with Strongly Oxidizing I(III) PhI(L)₂ Reagents

We report the outcomes of the reactions of aromatic group 16 thiophene, selenophene, and tellurophene rings with the I­(III) oxidants PhI­(OAc)­(OTf) and [PhI­(Pyr)2]­[OTf]2 (Pyr = pyridine). In all reactions, oxidative processes take place, with generation of PhI as the reduction product. However, with the exception of tellurophene with PhI­(OAc)­(OTf), +4 oxidation state complexes are not observed, but rather a variety of other processes occur. In general, where a C–H unit is available on the 5-membered ring, an electrophilic aromatic substitution reaction of either −IPh or pyridine onto the ring occurs. When all positions are blocked, reactions with PhI­(OAc)­(OTf) give acetic and triflic anhydride as the identifiable oxidative byproducts, while [PhI­(Pyr)2]­[OTf]2 gives pyridine electrophilic aromatic substitution onto the peripheral rings. Qualitative mechanistic studies indicate that the presence of the oxidizable heteroatom is required for pyridine to act as an electrophile in a substantial manner.