A Finding on the Direct Regioselective Cyanation of BODIPY

Abstract

The first example of direct α-cyanation of a BODIPY core has been achieved on 3-(methoxycarbonyl)ethenyl BODIPY. The structure of α-cyanated BODIPY was confirmed by X-ray analysis. Further cyanation took place on the meso-carbon of BODIPY.

Key words

BODIPY - cyanation - nucleophilic aromatic substitution - hydrogen substitution - regioselective substitution

• References and Notes

• 1 New Address: Chemistry Department, Polatli Faculty of Science and Letters, Ankara Haci Bayram Veli University, 06900 Polatli, Ankara, Turkey.
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• 10a Synthesis of 4: BODIPY 3 (10.3 mg, 0.025 mmol) was dissolved in acetonitrile (2 mL) and tetrabutylammonium cyanide (16.8 mg, 0.0625 mmol) was added to this solution at room temperature. After stirring for 30 min, the solvent was evaporated in vacuo. The crude product was purified by flash column chromatography (hexane/EtOAc, 5:1 to 2:1, v/v) to give 4 (3.5 mg, 34%) as a deep-red powder. ¹H NMR (400 MHz, CDCl₃): δ = 8.16 (s, 1 H), 7.60–7.45 (m, 5 H), 7.04 (d, J = 4.6 Hz, 2 H), 6.88 (d, J = 3.8 Hz, 2 H), 6.80 (d, J = 3.8 Hz, 2 H), 6.75 (d, J = 4.6 Hz, 2 H), 3.85 (s, 3 H), 3.82 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 165.8, 163.2, 155.2, 148.2, 138.9, 136.2, 135.4, 132.9, 132.8, 131.9, 130.7, 129.1, 128.9, 128.6, 124.2, 122.4, 121.2, 112.6, 53.4, 53.2. ¹⁹F NMR (376 MHz, CDCl₃): δ = –141.22 (dd, J = 59.8, 29.8 Hz). HRMS (ESI-TOF): m/z [M + Na]⁺ calcd for C₂₂H₁₆BF₂N₃O₄Na: 458.1094; found: 458.1113.
• 10b CCDC 1943830 contains the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
• 11 Synthesis of 5: BODIPY 4 (11.6 mg, 0.027 mmol) was dissolved in acetonitrile (2 mL) and tetrabutylammonium cyanide (10.7 mg, 0.040 mmol) was added to this solution at room temperature. After stirring for 10 min, the solvent was evaporated in vacuo. The crude product was purified by flash column chromatography (EtOAc) to give 5 (11 mg) as a pale-yellow viscous oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.21 (s, 1 H), 7.29–7.19 (m, 5 H), 6.74 (d, J = 3.4 Hz, 1 H), 6.56 (d, J = 3.7 Hz, 1 H), 6.06 (d, J = 3.7 Hz, 1 H), 5.97 (d, J = 3.4 Hz, 1 H), 3.78 (s, 3 H), 3.63 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 168.4, 140.8, 136.5, 136.2, 135.5, 128.8, 128.3, 128.2, 126.0, 122.6, 120.0, 117.1, 111.6, 108.8, 101.4, 52.7, 44.9. ¹⁹F NMR (376 MHz, CDCl₃): δ = –137.52 (m). The integrals of TBA⁺ in ¹H NMR spectra did not match the expected values in purified 5. Performing further silica gel column chromatography on 5 decreased these values (see the Supporting Information). This observation could be attributed to counter-ion change on the silica gel surface during purification. Thus, the proton and carbon peaks of the counter ion (TBA⁺) and percent yield are not given in the experimental data. HRMS (ESI-TOF): m/z [M – TBA]^– calcd for C₂₃H₁₆BF₂N₄O₄: 460.1269; found: 460.1289.
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