p-Selective (sp²)-C–H functionalization for an acylation/alkylation reaction using organic photoredox catalysis

Abstract

p-Selective (sp)-C-H functionalization of electron rich arenes has been achieved for acylation and alkylation reactions, respectively, with acyl/alkylselenides by organic photoredox catalysis involving an interesting mechanistic pathway.

Beyond Friedel and Crafts: Directed Alkylation of C−H Bonds in Arenes

“…[199] Upon excitation with visible light, 9,10dimethoxyanthracene induces the generation of alkyl radicals from the corresponding selenides which then add onto various electron-rich unactivated arenes (via the corresponding arene radical cations) used in excess (5 equivalents) to provide the desired alkylated arenes in good yields and with high levels of regioselectivity for the para position. [199] Upon excitation with visible light, 9,10dimethoxyanthracene induces the generation of alkyl radicals from the corresponding selenides which then add onto various electron-rich unactivated arenes (via the corresponding arene radical cations) used in excess (5 equivalents) to provide the desired alkylated arenes in good yields and with high levels of regioselectivity for the para position.…”

“…In addition to the use of alkenes,alkyl halides,alkylmetal reagents,and cross-dehydrogenative coupling reactions,some transformations have indeed recently been reported for the direct alkylation of unactivated arenes using less conventional alkylating agents:t hese include benzylic alcohols or ethers, aldehydes and ketones, [188] peroxides, [160] diazo compounds, [198] and alkylselenides. [199] In addition to the use of styrenes,Peris also reported that benzylic alcohols or ethers can act as efficient reagents for the direct benzylation of toluene and anisole derivatives in the presence of [IrCp*(OTf) 2 (I nBu )] (Scheme 76). [188] Thes ame catalyst could also promote at andem reaction in which aldehydes and ketones can be utilized as alkylating agents through an in situ reduction to the corresponding alcohols,the actual alkylating agents.Overall, the desired alkylated arenes are obtained in good yields and moderate to good ortho/para selectivities.…”

“…Finally,P andey reported the para-selective alkylation of simple arenes with alkylselenides using photoredox catalysis (Scheme 79). [199] Upon excitation with visible light, 9,10dimethoxyanthracene induces the generation of alkyl radicals from the corresponding selenides which then add onto various electron-rich unactivated arenes (via the corresponding arene radical cations) used in excess (5 equivalents) to provide the desired alkylated arenes in good yields and with high levels of regioselectivity for the para position. Theauthors rationalize the para selectivity by the arene radical cation being delocalized to form ad istal radical cation, with the structure having the radical character at the para position being the most stable one.…”

Beyond Friedel and Crafts: Innate Alkylation of C−H Bonds in Arenes

“…In addition to the use of alkenes, alkyl halides, alkylmetal reagents, and cross‐dehydrogenative coupling reactions, some transformations have indeed recently been reported for the direct alkylation of unactivated arenes using less conventional alkylating agents: these include benzylic alcohols or ethers, aldehydes and ketones, peroxides, diazo compounds, and alkylselenides …”

“…Finally, Pandey reported the para ‐selective alkylation of simple arenes with alkylselenides using photoredox catalysis (Scheme ) . Upon excitation with visible light, 9,10‐dimethoxyanthracene induces the generation of alkyl radicals from the corresponding selenides which then add onto various electron‐rich unactivated arenes (via the corresponding arene radical cations) used in excess (5 equivalents) to provide the desired alkylated arenes in good yields and with high levels of regioselectivity for the para position.…”