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. 2017 May 1;8(5):3618-3622.
doi: 10.1039/c6sc05533h. Epub 2017 Feb 27.

Mild, visible light-mediated decarboxylation of aryl carboxylic acids to access aryl radicals

L Candish  1 , M Freitag  1 , T Gensch  1 , F Glorius  1
Affiliations

Mild, visible light-mediated decarboxylation of aryl carboxylic acids to access aryl radicals

L Candish et al. Chem Sci. .

Abstract

Herein we present the first example of aryl radical formation via the visible light-mediated decarboxylation of aryl carboxylic acids using photoredox catalysis. This method constitutes a mild protocol for the decarboxylation of cheap and abundant aryl carboxylic acids and tolerates both electron-rich substrates and those lacking ortho-substitution. The in situ formation of an acyl hypobromite is proposed to prevent unproductive hydrogen atom abstraction and trapping of the intermediate aroyloxy radical, enabling mild decarboxylation.

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Figures

Scheme 1
Scheme 1. Challenges of photoredox-catalysed decarboxylation of aryl carboxylic acids and this approach to achieve a mild decarboxylation protocol.
Chart 1
Chart 1. Screen of different bromination reagents. General reaction conditions: reactions were performed using 4a (0.1 mmol), PC (3 mol%), Cs2CO3 (2 equiv.), [Br] (3.5 equiv.), arene (2.2 mL), blue LED (λ max = 455 nm), 55 °C, 22 h. Yields determined by GC-MS using decane as standard.
Scheme 2
Scheme 2. Scope of the biaryl synthesis. General reactions conditions; benzoic acid (0.2 mmol), PC (3 mol%), Cs2CO3 (2 equiv.), 5 (3.5 equiv.), arene (4.5 mL), blue LED (λ max = 455 nm), 55 °C, 22 h. Isolated yields (average of two reactions) following column chromatography. aReactions were performed with arene (150 equiv.) in CH3CN (1 : 1 v/v). bReactions were performed on 1.5 mmol scale, reaction time = 60 h. cReactions were performed with blue LED (λ max = 415 nm) at 80 °C. d2 equiv. 5 used. eReactions were performed using 23 W CFL. fRatio of isomers determined by GC-MS. gRatio of isomers determined by 19F NMR spectroscopic analysis of the crude mixture.
Scheme 3
Scheme 3. Proposed reaction mechanism. Counterions and ligand sphere of Ir are omitted for clarity.
Scheme 4
Scheme 4. (a) Trapping of the intermediate aroyloxy radical; (b) comparison of selectivities for biaryl formation, ratio determined by 19F NMR spectroscopic analysis; (c) visible light-mediated decarboxylation of 4a at elevated temperatures.
See this image and copyright information in PMC

References

    1. . For recent reviews on the visible light-promoted decarboxylation of alkyl carboxylic acids see;

    2. Liu J., Liu Q., Yi H., Qin C., Bai R., Qi X., Lan Y., Lei A. Angew. Chem., Int. Ed. 2014;53:502. - PubMed
    3. Miyake Y., Nakajima K., Nishibayashi Y. Chem. Commun. 2013;49:7854. - PubMed
    4. Zuo Z., MacMillan D. W. C. J. Am. Chem. Soc. 2014;136:5257. - PMC - PubMed
    5. Xuan J., Zhang Z.-G., Xiao W.-J. Angew. Chem., Int. Ed. 2015;54:15632. - PubMed
    6. Huang H., Jia K., Chen Y. ACS Catal. 2016;6:4983.
    7. Griffin J. D., Zeller M. A., Nicewicz D. A. J. Am. Chem. Soc. 2015;137:11340. - PMC - PubMed
    8. Candish L., Pitzer L., Gómez-Suárez A., Glorius F. Chem.–Eur. J. 2016;22:4753. - PubMed
    9. Candish L., Standley E. A., Gómez-Suárez A., Mukherjee S., Glorius F. Chem.–Eur. J. 2016;22:9971. - PubMed
    10. Millet A., Lefebvre Q., Rueping M. Chem.–Eur. J. 2016;22:13464. - PubMed

    1. For selected reviews on visible light photoredox catalysis, see:

    2. Zeitler K. Angew. Chem., Int. Ed. 2009;48:9785. - PubMed
    3. Narayanam J. M. R., Stephenson C. R. J. Chem. Soc. Rev. 2011;40:102. - PubMed
    4. Tucker J. W., Stephenson C. R. J. J. Org. Chem. 2012;77:1617. - PubMed
    5. Xuan J., Xiao W.-J. Angew. Chem., Int. Ed. 2012;51:6828. - PubMed
    6. Shi L., Xia W. Chem. Soc. Rev. 2012;41:7687. - PubMed
    7. Fukuzumi S., Ohkubo K. Chem. Sci. 2013;4:561.
    8. Hari D. P., König B. Angew. Chem., Int. Ed. 2013;52:4734. - PubMed
    9. Xi Y., Yi H., Lei A. Org. Biomol. Chem. 2013;11:2387. - PubMed
    10. Prier C. K., Rankic D. A., MacMillan D. W. C. Chem. Rev. 2013;113:5322. - PMC - PubMed
    11. Xuan J., Lu L.-Q., Chen J.-R., Xiao W.-J. Eur. J. Org. Chem. 2013:6755.
    12. Reckenthäler M., Griesbeck A. G. Adv. Synth. Catal. 2013;355:2727.
    13. Hopkinson M. N., Sahoo B., Li J.-L., Glorius F. Chem.–Eur. J. 2014;20:3874. - PubMed
    14. Koike T., Akita M. Top. Catal. 2014;57:967.
    15. Nicewicz D. A., Nguyen T. M. ACS Catal. 2014;4:355.
    16. Meggers E. Chem. Commun. 2015;51:3290. - PubMed
    17. Romero N. A., Nicewicz D. A. Chem. Rev. 2016;116:10075. - PubMed
    18. Skubi K. L., Blum T. R., Yoon T. P. Chem. Rev. 2016;116:10035. - PMC - PubMed
    1. Ghosh I., Marzo L., Das A., Shaikh R., König B. Acc. Chem. Res. 2016;49:1566. - PubMed
    1. Yasu Y., Koike T., Akita M. Adv. Synth. Catal. 2012;354:3414.
    1. Seiple I. B., Su S., Rodriguez R. A., Gianatassio R., Fujiwara Y., Sobel A. L., Baran P. S. J. Am. Chem. Soc. 2010;132:13194. - PMC - PubMed
    2. Barton D. H. R., Ramesh M. Tetrahedron Lett. 1990;31:949.
    3. Barton D. H. R., Lacher B., Zard S. Z. Tetrahedron. 1987;43:4321.