Organic Dye-Catalyzed Aerobic Photooxidation of Benzylic C—H Bonds

doi:10.6023/cjoc202601037

Abstract

Photooxygenation of benzylic C(sp³)—H bonds by oxygen occurs efficiently under photoirradiation using Eosin Y as a photocatalyst to yield aldehydes and ketones. This method is able to activate alkylarenes such as toluene and can overcome overoxidation into carboxylic acids. This approach features an inexpensive photocatalyst, broad substrate scope, easy scale-up and further transformation. In addition, the photophysical characteristics of the Eosin Y and the reaction mechanism were also discussed.

Key words: photocatalysis, Eosin Y, benzylic C(sp³)—H, aldehyde, ketone

Cite this article

Wenjing Li, Chunye Liu, Lingling Liang, Yanqing Miao, Jing You, Siyu Shen. Organic Dye-Catalyzed Aerobic Photooxidation of Benzylic C—H Bonds[J]. Chinese Journal of Organic Chemistry, 2026, 46(10): 4172-4181.

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Fig. & Tab. 11

Figure 1. Examples of prodrugs containing ketone moiety

Scheme 1. Methodologies for the oxidative benzylic C(sp3)—H bond

Entry	Wavelength/nm	Photocatalyst	Oxidant	Yield/%
1	365	Fluorescein	TBHP	Trace
2	365	Na₂-Eosin Y	TBHP	50
3	365	Rhodamine 6G	TBHP	37
4	365	Rhodamine B	TBHP	Trace
5	365	Dibromofluorescein	TBHP	44
6	365	Eosin Y	TBHP	65
7	365	Eosin Y	O₂	36
8	365	Eosin Y	Air	20
9^c	365	Eosin Y	TBHP	76
10	365	—	TBHP	n.d.
11	390	Eosin Y	TBHP	44
12	425	Eosin Y	TBHP	31
13	450	Eosin Y	TBHP	24

Table 1. Optimization of reaction conditionsa,b

Table 2. Photocatalytic oxidative benzylic C(sp3)—H to aldehydesa,b

Table 3. Photocatalytic oxidative benzylic C(sp3)—H to ketonesa,b

Scheme 2. Scale-up reaction and synthesis applications

Scheme 3. Isotope-labelling experiments

Scheme 4. Control experiments

Figure 2. On/off experiments

Figure 3. (a) Fluorescence quenching of excited Eosin Y by toluene S1 in CH3CN; (b) Stern-Volmer plots for the fluorescence quenching of Eosin Y with toluene

Scheme 5. Proposed mechanism

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有机染料催化苄基C—H键的有氧光氧化