Synlett 2016; 27(05): 741-744
DOI: 10.1055/s-0035-1561342
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© Georg Thieme Verlag Stuttgart · New York

Reduction of Aryl Halides into Arenes with 2-Propanol Promoted by a Substoichiometric Amount of a tert-Butoxy Radical Source

Ryota Ueno
a  Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Kyoto 606-8502, Japan
,
Takashi Shimizu
a  Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Kyoto 606-8502, Japan
,
Eiji Shirakawa*
b  Department of Applied Chemistry for Environment, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan   Email: eshirakawa@kwansei.ac.jp
› Author Affiliations
Further Information

Publication History

Received: 01 December 2015

Accepted after revision: 11 January 2016

Publication Date:
27 January 2016 (online)


Abstract

Aryl halides are reduced into the corresponding arenes in high yields, using 2-propanol, cesium carbonate, and di-tert-butyl peroxide (or di-tert-butyl hyponitrite) as a reductant/solvent, a base, and a radical initiator, respectively. This simple system reduces a wide variety of aryl bromides, chlorides, and iodides through single-electron-transfer mechanism with high functional-group tolerance.

Supporting Information

 
  • References and Notes

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    • 1b Safe SH. Crit. Rev. Toxicol. 1994; 85: 131
  • 2 For overview on the methods to reduce aryl halides into arenes, see: Smith MB. March's Advanced Organic Chemistry . Wiley; Hoboken: 2013. 7th ed., 647-648
  • 3 For a recent example, see: Bhattacharjya A, Klumphu P, Lipshutz BH. Org. Lett. 2015; 17: 1122 ; and references cited therein
    • 4a Bunnett JF, Wamser CC. J. Am. Chem. Soc. 1967; 89: 6712
    • 4b Tomaselli GA, Cui J.-J, Chen Q.-F, Bunnett JF. J. Chem. Soc., Perkin Trans. 2 1992; 9
    • 4c Tomaselli GA, Bunnett JF. J. Org. Chem. 1992; 57: 2710
    • 4d Bunnett JF. Acc. Chem. Res. 1992; 25: 2

      A combination of LiAlH4 as a reductant with t-BuOOt-Bu as a radical initiator is used for reduction of aryl halides under photoirradiation, see:
    • 5a Beckwith AL. J, Goh SH. J. Chem. Soc., Chem. Commun. 1983; 905
    • 5b Beckwith AL. J, Goh SH. J. Chem. Soc., Chem. Commun. 1983; 907
  • 6 p-Methoxyphenyl radical possibly reacts also with anisole (2a). However, it would give p-(p-methoxyphenyl)anisole in addition to ortho and meta isomers. No generation of the para isomer shows that such a reaction hardly took place under the reaction conditions.
  • 7 The half-life of t-BuOOt-Bu is reported to be more than 1000 h even at 80 °C. See: Walling C. Tetrahedron 1985; 41: 3887
  • 8 t-BuON=NOt-Bu is reported to undergo decomposition into t-BuO and N2 with t 1/2 = 29 min at 65 °C. See: Kiefer H, Traylor TG. Tetrahedron Lett. 1966; 7: 6163
  • 9 General Procedure To a 3 mL vial equipped with a stir bar in a glove box were added successively an aryl halide 1 (0.25 mmol), 2-PrOH (1.5 mL, 0.020 mol), Cs2CO3 (97.7 mg, 0.30 mmol), and t-BuOOt-Bu (8.8 mg, 0.050 mmol). The vial was taken out of the glove box and stirred at 120 °C for 3 or 24 h. Decane was added to the reaction mixture as an internal standard for GC analysis. After dilution with EtOAc (1.0 mL), an aliquot was subjected to GC analysis. For products having a boiling point that is high enough not to be lost in evacuation process, addition of H2O (20 mL) was followed by extraction with EtOAc (3 × 20 mL). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The residue was subjected to silica gel chromatography (PTLC) to give the corresponding arene 2.