Heteroarene radical functionalization

Because C-H bonds are usually less reactive towards dioxirane oxidation than heteroatoms and C-C multiple bonds, it is instructive to give a few general guidelines on the compatibility of functional groups within the substrate to be submitted to oxidative C-H insertion Substances with low-valent heteroatoms (N, P, S, Se, I, etc.), C-C multiple bonds, and C=X groups (where X is a N or S heteroatom) are normally not suitable for C-H insertions, because these functionalities react preferably. Even heteroarenes are more susceptible to dioxirane oxidation than C-H bonds, whereas electron-rich and polycyclic arenes are only moderately tolerant, but electron-poor arenes usually resist oxidation by dioxiranes. N-oxides and N-oxyl radicals are not compatible because they catalyze the decomposition of the dioxirane. Oxygen insertion into Si-H bonds by dioxirane is more facile than into C-H bonds and, therefore, silanes are not compatible. Substance classes normally resistant towards dioxirane oxidation include the carboxylic acids and their derivatives (anhydrides, esters, amides, and nitriles), sulfonic acids and their de-... 

Heteroarenes have been photochemically functionalized by PET reactions forming new C—C bonds both in an inter- and intramolecular fashion via a similar mechanism [46]. The heteroarenes could serve both as electron donor (e.g. pyrroles or indoles) or electron acceptor (e.g. cyanopyridines or cyanopyrazines). Again, fragmentation of the radical cation, coupled with the radical anion and loss of the anion, led to overall ipso-substitution. In addition to the cyano group, halides could also function as leaving groups, such that in some cases an attack at an unsubstituted position took place [46],... 

O Hara F, Blackmond DG, Baran PS. Radical-based regioselective C-H functionalization of electron-deficient heteroarenes scope, tunabihty, and predictability. JAm Chem Soc. 2013 135 12122-12134. 

Heteroarene Functionalization One-pot Sequential Functionalization Chemistry. Zinc isopropylsuUinate can be considered as a radical with nucleophilic character. Zinc trifluoromethanesulfinate (TFMS), another zinc bis(alkanesulfinate) reagent, possesses a rather electrophilic character. By taking advantage of the electrophiUcity/ nucleophiUcity of the reactive radical species, a one-pot sequential functionalization reaction was developed. Dihydroquinine can undergo tandem trifluoromethylation and isopropylation without the need for secondary alcohol protection (eq 7). 

Heteroarene Functionalization One-pot Sequential Functionalization Chemistry. The title reagent can behave as a radical with electrophilic character. In contrast, zinc... 

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