Tandem oxidation processes on activated alcohols using MnO₂; Methyl esters

Jonathan Foot ([email protected]),
A contribution from the Taylor Group, York

Chemicals Used
Activated manganese(IV) oxide (Aldrich, cat no. 21,764-6, <5 micron, activated 85%) tetrahydrofuran (distilled over sodium and benzophenone) methanol (Fluka, analytical grade) cinnamyl alcohol (Aldrich, 99%) sodium cyanide (Aldrich, 99%).

Procedure
To a mixture of cinnamyl alcohol (0.134 g, 1 mmol) and sodium cyanide (0.049 g, 1 mmol) stirring in THF (10 mL) at ambient temperature and pressure, was added manganese(IV) oxide (1.34 g, 15 mmol). The reaction was heated at reflux for 5 hours. The resulting mixture was then filtered through a pad of Celite® and the solvent removed under reduced pressure. Extraction with dichloromethane (50 mL) was followed by washing with water (2 x 10 mL) and then saturated sodium chloride solution (10 mL), before drying the organic layer over magnesium sulfate. Filtration and removal of solvent in vacuo gave methyl trans-cinnamate (0.113 g, 70%) as light yellow crystals.

Author's Comments
This procedure can be applied to a wide range of activated alcohols, and normally there is no need for additional chromatographic purification. Higher yields can be obtained by carrying out the reaction at room temperature, in methanol containing acetic acid, but longer reaction times are required (up to 7 days). Amides can be prepared directly from activated alcohols in a similar procedure (see lead reference).

Data
¹H nmr (270 MHz, CDCl₃) 3.82 (3 H, s), 6.43 (1 H, d, J 16.0 Hz), 7.41 (3 H, m), 7.54 (2 H, m), 7.71 (1 H, d, J 16.0 Hz). m.p. 35°C.

Lead Reference
Foot, J.S., Kanno, H., Giblin, G.M.P., Taylor, R.J.K, Synlett, 2002, 8, 1239

Other References
Blackburn, L., Wei, X., Taylor, R. J. K., Chem. Commun. 1999, 1337. Wei, X., Taylor, R. J. K., J. Org. Chem. 2000, 65, 616. Blackburn, L., Taylor, R. J. K., Org. Lett. 2001, 3, 1637. Blackburn, L., Pei, C., Taylor, R. J. K., Synlett 2002, 2, 215. Runcie, K.A., Taylor, R. J. K., Chem. Commun., 2002, 974. Kanno, H., Taylor, R. J. K., Synlett, 2002, 8, 1287. McAllister, G. D., Wilfred, C. D., Taylor, R. J. K., Synlett, 2002, 8, 1291.

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