Brønsted acid-enhanced direct hydrogen atom transfer photocatalysis for selective functionalization of unactivated C(sp3)–H bonds

Eosin Y mediated photo-catalytic C–H functionalization: C–C and C–S bond formation

“…25 During substrate scope screening, the authors found that malonates with methyl and ethyl groups were well reacted. In addition, substitutions such as -Br, -CH 3 , -OCH 3 on the aromatic ring at different positions gave the corresponding scaffolds (45,46) in good yields (Scheme 22). Notably, the reaction followed the SET mechanism, but photoexcited eosin Y was reduced by tetrahydroisoquinoline.…”

“…To find mechanistic insight they performed several control experiments that suggested the hydrogen atom transfer mechanism. 45…”

Heteroarylation of unactivated C–H bonds suitable for late-stage functionalization

“… 11 These transformations also require the use of substrate in large excess and feature poorly selective HAT reagents which are undesirable in applications involving complex substrates with multiple reactive sites. 12 Additionally, C–H heteroarylations involving Minisci-type additions can suffer from poor regio- and chemoselectivity in the radical addition, leading to mixtures of products and, in certain cases, overalkylation. 13 …”

Photocatalytic Incorporation of an Oxime Ether Functional Group at Inert C(sp3)–H Bonds via HAT

“…Under the standard conditions, the reaction of cyclohexane and 1a gave only a trace amount of the desired product, most likely due to inefficient HAT from the alkanes to photoexcited EY. Recently, it was demonstrated that the HAT efficiency of photoexcited EY could be improved by protonation with a suitable Brønsted acid . Following this report the oximes 43 – 45 were synthesized via the reaction of 1a with alkanes using modified reaction conditions in the presence of PTSA.…”

“…Recently, it was demonstrated that the HAT efficiency of photoexcited EY could be improved by protonation with a suitable Brønsted acid. 14 Following this report the oximes 43−45 were synthesized via the reaction of 1a with alkanes using modified reaction conditions in the presence of PTSA.…”