Efficient Synthesis of Anthraquinones from Diaryl Carboxylic Acids via Palladium(II)‐Catalyzed and Visible Light‐Mediated Transformations

Abstract

Irradiation of 9-ester-substituted anthracenes with visible light results in the formation of endoperoxides in the absence of a photocatalyst, which further undergo base-assisted fragmentation to afford anthraquinones. The excited state species of anthracene generated by energy transfer, interacts with 3 O 2 to afford 1 O 2 by energy transfer and undergoes cycloaddition with 1 O 2 . By employing palladium(II)-catalyzed and visible light-mediated transformations, we have developed an efficient synthetic protocol for accessing diverse anthraquinones from readily available diaryl carboxylic acids. The optimal result was obtained with palladium(II) acetate, Ac-Ile-OH, benzoquinone and potassium carbonate in tert-amyl alcohol under O 2 at 90 8C with irradiation from a 30 W fluorescent light bulb.

Lewis Acid-Catalyzed Benzannulation of Vinyloxiranes with 3-Formylchromones or 1,4-Quinones for Diversely Functionalized 2-Hydroxybenzophenones, 1,4-Naphthoquinones, and Anthraquinones

“…1 H NMR (600 MHz, CDCl 3 ) δ 8.33–8.31 (m, 2H), 8.28–8.26 (m, 2H), 7.83–7.82 (m, 2H), 7.75 (dd, J = 8.4, 2.4 Hz, 1H); 13 C­{ 1 H} NMR (150 MHz, CDCl 3 ) δ 182.3, 182.2, 141.3, 134.8, 134.6, 134.4, 134.3, 133.4, 133.4, 131.9, 129.2, 127.5, 127.5, 127.3. The 1 H and 13 C NMR data corresponded with reported literature data …”

Recent advances in the syntheses of anthracene derivatives

“…In a direct comparison with the methodology proposed by Hong for the synthesis of anthracenes, previously shown in Scheme 7 [ 41 ], the key to obtaining anthraquinones was the photooxidation induced by visible light, which afforded the substituted anthraquinones 194 . In this case, the effect of the aromatic ring substituents also affected the yield of the anthraquinones, as can be seen from the representative examples 194a – d [ 81 ].…”

“…In 2017, Hong and co-workers reported another efficient protocol for the direct synthesis of substituted anthraquinones ( Scheme 45 ) [ 81 ]. The authors employed palladium(II) acetate and visible light under O 2 in the reactions between ethyl acrylate ( 192 ) and substituted diaryl carboxylic acids 193 , to produce anthraquinones 194 in low to moderate yields (30–68%).…”

Is Emodin with Anticancer Effects Completely Innocent? Two Sides of the Coin

“…Synthetic approaches to anthraquinone skeletons are the subject of much investigation, where a few synthetic strategies have been improved to obtain this family of compounds using a variety of catalytic systems. Nowadays, most the processes displayed remarkable deficiencies like the need for multiple synthetic steps, harsh reaction conditions, and regioselectivity issues [ 173 ].…”