Visible Light‐Induced Decarboxylative Alkylation of Heterocyclic Aromatics with Carboxylic Acids via Anthocyanin as a Photocatalyst

Abstract

A visible light‐induced decarboxylative alkylation of heterocyclic aromatics with aliphatic carboxylic acids was developed by using anthocyanins as a photocatalyst under mild conditions. A series of alkylated heterocyclic compounds were obtained in moderate to good yields by using the metal‐free decarboxylative coupling reaction under blue light. This strategy uses cheap and readily available carboxylic acids as alkylation reagents with good functional group tolerance and environmental friendliness. It is worth noting that this is the first time that anthocyanin has been used to catalyze the Minisci‐type C−H alkylation. The mechanism of decarboxylation alkylation was studied by capturing the adduct of alkyl radical and hydroquinone, thus confirming a radical mechanism. This protocol provides an alternative visible light‐induced decarboxylative alkylation for the functionalization of heterocyclic aromatics.

Advances in Photoinduced Minisci-like Reactions

“…40 In this regard, a visible-light-promoted decarboxylative Minisci-type reaction was reported to proceed via oxidative quenching of the excited state of anthocyanin using ammonium persulfate, according to quenching studies (Scheme 10a ). 41 The formed sulfate radical anion was proposed to promote the deprotonation and oxidation of the starting carboxylic acids, forming an alkyl radical after decarboxylation. Adding this radical to the heteroarene, followed by SET to recover the ground state of the photocatalyst, afforded the corresponding coupling products with moderate to good yields.…”