Synlett 2019; 30(15): 1799-1804
DOI: 10.1055/s-0039-1690018
letter
© Georg Thieme Verlag Stuttgart · New York

CF3COOH/O2-Mediated Metal-Free Domino Construction of the Isatin Skeleton

Jiadi Zhou
a   Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
,
Yongjian Chen
a   Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
,
Fang Wang
b   College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, P. R. of China   Email: lijianjun@zjut.edu.cn
,
Qiwei Zhang
b   College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, P. R. of China   Email: lijianjun@zjut.edu.cn
,
Jianjun Li
a   Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
b   College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, P. R. of China   Email: lijianjun@zjut.edu.cn
› Author Affiliations
We are grateful to the National Natural Science Foundation of China (No. 21776254) for financial help.
Further Information

Publication History

Received: 18 June 2019

Accepted after revision: 28 July 2019

Publication Date:
14 August 2019 (online)


Abstract

Directed by the strategy of C–H activation, an efficient construction of the isatin skeleton was developed through aerobic oxidation of glycine esters. The reactions were performed under CF3COOH/O2 conditions in the absence of metal catalysts. The reaction mechanisms were investigated with control experiments.

Supporting Information

 
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  • 9 Intramolecular Cyclization; General Procedure A: A 25 mL round-bottom flask containing N-alkyl-N-arylglycinate (1 mmol), CF3COOH (0.5 mmol), and MeCN (5 mL) was stirred at 70 °C under O2 (1 atm) for 12 h. CF3COOH (0.5 mmol) was added and, after stirring for 36 h, the reaction mixture was concentrated under reduced pressure and the crude product was purified by column chromatography on silica gel.5-Methoxy-1-methylindoline-2,3-dione (2i)Prepared by following General Procedure A using ethyl N-(4-methoxyphenyl)-N-methylglycinate (223 mg, 1.0 mmol). Purification by column chromatography (n-hexane/EtOAc, 5:2) gave 2i (120 mg, 63%) as a red solid. 1H NMR (400 MHz, CDCl3): δ = 7.17–7.13 (m, 2 H), 6.82 (d, J = 8.4 Hz, 1 H), 3.81 (s, 3 H), 3.22 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 183.7, 158.3, 156.6, 145.3, 124.6, 117.8, 110.9, 109.6, 56.0, 26.2. HRMS (ESI+): m/z [M +  Na]+ calcd for C10H9NNaO3: 214.0475; found: 214.0476.
  • 10 Intermolecular Cyclization; General Procedure B: A 25 mL round-bottom flask with N-H-N-arylglycinate (1 mmol), CF3COOH (0.5 mmol) and MeCN (5 mL) was stirred at 70 °C under O2 (1 atm) for 6 h. CF3COOH (0.5 mmol) was added and, after stirring for 6 h, the reaction mixture was concentrated under reduced pressure and the crude product was purified by column chromatography on silica gel.Methyl 2-(5-Isopropyl-2,3-dioxoindolin-1-yl)acetate (4b)Prepared by following General Procedure B using methyl (4-isopropylphenyl) glycinate (207 mg, 1.0 mmol). Purification by column chromatography (n-hexane/EtOAc, 8:1) gave 4b (98 mg, 75%) as a red solid. 1H NMR (400 MHz, CDCl3): δ = 7.53 (s, 1 H), 7.46 (d, J = 8.1 Hz, 1 H), 6.74 (d, J = 8.1 Hz, 1 H), 4.49 (s, 2 H), 3.79 (s, 3 H), 2.90 (hept, J = 6.8 Hz, 1 H), 1.24 (d, J = 6.9 Hz, 6 H). 13C NMR (101 MHz, CDCl3): δ = 182.8, 167.4, 158.3, 148.3, 145.3, 136.8, 123.4, 117.7, 110.0, 52.8, 41.1, 33.5, 23.8 (2C). MS (ESI+): m/z = 262.05 [M + H]+. HRMS (ESI+): m/z [M + Na]+ calcd for C14H15NNaO4: 284.0893; found: 284.0889.
  • 11 Detailed analysis conditions for intermediates I: A 25 mL round-bottom flask containing 1a (1 mmol), CF3COOH (0.5 mmol), TEMPO (1 equiv), and MeCN (5 mL) was stirred at 70 °C under O2 (1 atm) for 12 h. The reaction mixture was concentrated under reduced pressure and the crude material was analyzed by HRMS-APCI using ESI+ ionization.Detailed analysis conditions for intermediates D, E, F, and H: To a 25 mL round-bottom flask containing 3g (1 mmol), CF3COOH (0.5 mmol), and MeCN (5 mL) was stirred at 70 °C under O2 (1 atm) for 2 h, then the reaction mixture was concentrated under reduced pressure and the crude material was analyzed by HRMS-APCI using ESI+ ionization.