“…Interestingly, TPT• can react with 3 O 2 to give peroxyl radical 48.3 (Scheme ), which is implicated as an intermediate in some oxygenation reactions enabled by TPT + , although others have argued against such an intermediate . Despite the moderate ground state reduction potential enabling TPT• to be returned to the ground state TPT + by a relatively weak oxidant, pyranyl radicals are prone to dimerization adducts 48.1 , − which, although reversible for 2,4,6-triarylpyryliums, can deactivate the catalyst in an off-cycle equilibrium. Likewise, nucleophiles can add to the pyrylium core and lead to catalyst degradation via the formation of addition adducts such as 48.2 …”