Electrochemical Deoxygenation of Primary Alcohols

Abstract

Direct electrolysis of primary alcohols, in the presence of methyl toluate, leads smoothly to the formation of the corresponding deoxygenated product in high yield.

Key words

deoxygenation - electrochemical - esters - reduction - free radicals

• References and Notes

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• 1b For a review, see: Hartwig W. Tetrahedron 1983; 39: 2609
• 2 Zard ZS. Angew. Chem. Int. Ed. 1997; 36: 672
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• 4 Barton DH. R, Doo OJ, Jaszberényi JC. Tetrahedron Lett. 1992; 33: 5709
• 5 Large-scale Barton–McCombie deoxygenation reactions suffer from reproducibility issues, difficulties to scale-up, instability of the xanthate, toxicity of the by-products and also economic concerns
• 6 Lam K, Markó IE. Org. Lett. 2008; 10: 2773
• 7a Lam K, Markó IE. Chem. Commun. 2009; 95
• 7b Lam K, Markó IE. Tetrahedron 2009; 65: 10930
• 8 Electrochemical reduction of secondary and tertiary toluates gave 64–85% yield of deoxygenated product
• 9 Electrochemical reduction of primary toluates gave 33–41% yield of deoxygenated product
• 10 Arai K, Tamura S, Masumizu T, Kawai K.-I, Ueda A, Nakajima S. Can. J. Chem. 1990; 68: 903
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• 13a Kurihara H, Tajima T, Fuchigami T. Electrochemistry 2006; 74: 615
• 13b Tajima T, Kurihara H, Fuchigami T. J. Am. Chem. Soc. 2007; 129: 6680
• 14 Typical Experimental Procedure: An H-type cell, with two compartments of 100 mL, separated by a sintered glass with a porosity of 40 μm, was dried for one night at 200 °C. Then, each cell was equipped with graphite electrode of 6 cm² and a magnetic stir bar. Both compartments were then flushed with argon for 10 min. After filling them with NBu₄BF₄ (5 g) and with DMF (100 mL; freshly distilled under argon), primary alcohol (1 equiv) and methyl toluate (3 equiv) were added to the cathodic compartment and the solution was stirred and heated to 60 °C. Then, the intensity of the current was fixed at 600 mA and the mixture was electrolyzed until completion of the reaction, as shown by TLC or by GC (usually 6 h). The cell was then cooled to r.t. and the catholyte was carefully diluted with 4 M HCl (100 mL). The resulting solution was extracted with Et₂O (4 × 30 mL). The organic phases were collected, dried over Na₂SO₄ and the solvent was removed under reduced pressure. Finally, the crude product was purified by chromatography over silica gel to yield the desired deoxygenated product