Preparation of Aldehydes by Oxidation of Benzylic Amines with Selectfluor™ (F-TEDA-BF4)

Abstract

Aldehydes are obtained by mild oxidation of benzylic amines with Selectfluor™. The results are compared favorably with the Polonovski-like process using hypervalent iodine.

Key words

Selectfluor™ - amines - oxidation - aromatic aldehydes

• References and Notes

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Since our work for this manuscript was finished, two novel approaches for the oxidative deamination of benzylic amines have been published which should be mentioned here despite of the smaller reaction scope they cover. See:
• 8a Ling Z, Yun L, Liu L, Wu B, Fu X. Chem. Commun. 2013; 49: 4214
• 8b Gong JL, Qi X, Wei D, Feng J.-B, Wu X.-F. Org. Biomol. Chem. 2014; 12: 7486
• 9 Experimental Procedure To a suspension of 1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane ditetrafluoroborate (1, 0.975 mmol) in MeCN (3 mL) the amine (2, 0.75 mmol) dissolved in MeCN (3 mL) was added dropwise at r.t. The reaction was stirred at r.t. for another 20 min. The solvent was evaporated, and the obtained residue was purified via flash column chromatography using silica gel as stationary phase.
• 10 Benzaldehyde (5a) ¹H NMR (400 MHz, CDCl₃): δ = 10.05 (s, 1 H), 7.89–7.95 (m, 2 H), 7.63–7.69 (m, 1 H), 7.54–7.60 (m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ = 192.4, 136.5, 134.5, 129.8, 129.0 ppm. IR: ν = 3070 (m), 2837 (m), 2678 (w), 1559 (w), 1686 (vs) cm^–1. 3-Iodobenzaldehyde (5b) ¹H NMR (400 MHz, CDCl₃): δ = 9.95 (s, 1 H), 8.23 (t, J = 1.5 Hz, 1 H), 7.98 (dt, J = 7.6, 1.6 Hz, 1 H), 7.87 (dt, J = 7.8, 1.3 Hz, 1 H), 7.31 (t, J = 7.8 Hz, 1 H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ = 190.7, 143.2, 138.5, 138.1, 130.8, 128.9, 94.7 ppm. IR: ν = 3377 (w), 3057 (w), 2825 (m), 2727 (m), 1699 (vs) cm^–1. 4-Methoxybenzaldehyde (5c) ¹H NMR (400 MHz, CDCl₃): δ = 9.92 (s, 1 H), 7.87 (d, J = 8.8 Hz, 2 H), 7.01–7.06 (m, 2 H), 3.92 (s, 3 H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ = 190.8, 164.7, 132.0, 130.1, 114.4, 55.6 ppm. 4-Bromobenzaldehyde (5d) ¹H NMR (300 MHz, CDCl₃): δ = 10.00 (s, 1 H), 7.77 (dd, J = 6.4, 2.1 Hz, 2 H), 7.71 (dd, J = 6.8, 1.8 Hz, 2 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 191.0, 135.1, 132.4, 131.0, 129.8 ppm. IR: ν = 3350 (w), 3086 (m), 2860 (s), 1699 (vs), 1585 (vs), 1383 (vs), 835 (vs), 814 (s) cm^–1. 3-Bromobenzaldehyde (5d) ¹H NMR (400 MHz, CDCl₃): δ = 9.99 (s, 1 H), 8.04 (t, J = 1.8 Hz, 1 H), 7.83 (dt, J = 7.7, 1.2 Hz, 1 H), 7.78 (ddd, J = 7.9, 2.0, 1.0 Hz, 1 H), 7.45 (t, J = 7.8 Hz, 1 H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ = 190.7, 138.1, 137.3, 132.4, 130.7, 128.4, 123.4 ppm. IR: ν = 1695 (s), 1556 (s), 1252 (m), 754 (vs) cm^–1. 4-Nitrobenzaldehyde (5f) ¹H NMR (400 MHz, CDCl₃): δ = 10.18 (s, 1 H), 8.41 (d, J = 8.6 Hz, 2 H), 8.10 (d, J = 8.8 Hz, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ = 190.3, 151.2, 140.1, 130.5, 124.3 ppm. IR: ν = 3107 (w), 2850 (m), 1709 (vs), 1605 (m), 1539 (s), 1381 (m), 1346 (vs), 1327 (s), 1288 (m), 1105 (m), 1007 (w), 851 (s), 818 (s), 741 (s) cm^–1.