Hydrogen abstraction in the liquid phase by free radicals

Generation of Alkoxyl Radicals by Photoredox Catalysis Enables Selective C(sp3)−H Functionalization under Mild Reaction Conditions

“…[29] Theunactivated tertiary CÀHbonds also react smoothly to give 24 and 25 in 63 %and 58 %yield, respectively, [30] as they are slightly less reactive than those with neighboring activating groups. [31] As the alkoxyl radical is known to be highly reactive,w e next tested the regioselectivity of the reaction (Scheme 4): TheN -alkoxyphthalimide substrates with both d-a nd e-C(sp 3 )ÀHb onds give the d-C(sp 3 )ÀHa ctivation adducts 26 and 12 exclusively,a nd the e-C(sp 3 )ÀHf unctionalization adducts were not observed, thus showcasing the selectivity of the reaction. [32] Methine,m ethylene,a nd methyl C À Hb onds activated by an oxygen atom react well to give 26, 12, and 27, respectively.T he allyl acceptors can be extended to phenylsubstituted allyls and give the products 28-30 in 62-75 % yields.T his C(sp 3 )ÀHfunctionalization is not only applicable to C(sp 3 )ÀC(sp 3 )b ond formation, but also to C(sp 3 )ÀC(sp 2 ) bond formation.…”

Generation of Alkoxyl Radicals by Photoredox Catalysis Enables Selective C(sp3)−H Functionalization under Mild Reaction Conditions

“…[27] We next explored the substrate scope and found that the reaction works well for a-heteroatom-activated C À Hb onds, such as with para-methoxy substitution, to give the allylated 15 in 91 %y ield (reaction conditions:e ntry 8i nT able 1), whereas the para-fluoro and ortho-iodo substituents gave 16 (80 %) and 17 (76 %), respectively (Scheme 4). [31] As the alkoxyl radical is known to be highly reactive,w e next tested the regioselectivity of the reaction (Scheme 4): TheN -alkoxyphthalimide substrates with both d-a nd e-C(sp 3 )ÀHb onds give the d-C(sp 3 )ÀHa ctivation adducts 26 and 12 exclusively,a nd the e-C(sp 3 )ÀHf unctionalization adducts were not observed, thus showcasing the selectivity of the reaction. We explored whether heterocycles could be tolerated under the reaction conditions, as ubstrate class with which many C(sp 3 )ÀHa ctivation methods encounter difficulties.…”

Oxidative degradation of pharmaceuticals: Theory, mechanisms and inhibition

“…Correlation of the rate constant of hydrogen abstraction and the ability of a substituent to stabilize a polar transition state was demonstrated for hydrogen atom abstraction from substituted toluenes by tert ‐butoxyl radicals (Figure 3). 69 The transition state for hydrogen abstraction from CH bonds in the α‐position to a heteroatom (N, O, S, and P) is also sensitive to charge induction 70. Multiple substituents have more complex effects on the forming radical center.…”