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Biarylcarboxylic acid 1 (0.1 mmol), Ir[dF(CF3)ppy]2(dtbbpy)PF6
(2.3 mg, 0.02 mmol), Ph3P (78.6 mg, 0.3 mmol), K2CO3 (10.4 mg,
0.075 mmol) and DCE (2 mL) were added to a 10 mL Schlenk
tube equipped with a magnetic stir bar. The tube was placed at
a distance of ~5 cm from 2 blue LEDs (45 W) under air, and the
resulting solution was stirred for 24 h. After the reaction was
complete (monitored by TLC), the mixture was concentrated
under vacuum to remove DCE and the residue was purified by
silica gel column chromatography (hexane/EtOAc = 20:1 to 5:1)
to afford the product 2.
9H-Fluoren-9-one (2a)
Compound 2a (12.6 mg, 70%) was synthesized using the general
procedure and isolated as a yellow solid; mp 81–82 °C. 1H NMR
(500 MHz, CDCl3): = 7.66 (d, J = 7.3 Hz, 2 H), 7.53–7.47 (m, 4
H), 7.29 (td, J = 7.3, 1.2 Hz, 2 H). MS (EI): m/z (%) = 180.0 (100)
[M+].
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2-Methyl-9H-fluoren-9-one (2b)
Compound 2b (14 mg, 72%) was synthesized using the general
procedure and isolated as a yellow solid; mp 90–91 °C. 1H NMR
(500 MHz, CDCl3): = 7.63 (d, J = 7.3 Hz, 1 H), 7.47–7.44 (m, 3
H), 7.39 (d, J = 7.5 Hz, 1 H), 7.29–7.23 (m, 2 H), 2.37 (s, 3 H). MS
(EI): m/z (%) = 194.1 (100) [M+].
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(18) Flow Chemistry; General Procedure
.
Biarylcarboxylic acid 1a (198 mg, 1 mmol), PPh3 (786 mg, 3
mmol), K2CO3 (69 mg, 0.5 mmol, 120 mesh), and
Ir[dF(CF3)ppy]2(dtbbpy)PF6 (11.7 mg, 0.01 mmol) were placed
in a round-bottom flask (100 mL). DCE (30 mL) was added
under air and the mixture was pumped at a rate of 82 mL min–1
using a peristaltic pump under irradiation with 2 blue LEDs (45
W). After 8.5 h, the reaction was complete. The mixture was
concentrated under vacuum to remove DCE and the residue was
purified by silica gel column chromatography (hexane/EtOAc =
20:1 to 5:1) to afford the product 2a.
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© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–D