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Synlett 2008(15): 2309-2312  
DOI: 10.1055/s-2008-1078276
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Reinvestigation of Highly Diastereoselective Pentacyclic Spirolactone Formation by Direct Anodic Oxidation of 2,4-Dimethylphenol

Joaquin Barjaua, Pia Königsa, Olga Kataevab, Siegfried R. Waldvogel*a
a Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
e-Mail: waldvogel@uni-bonn.de;
b A. E. Arbuzov Institute of the Russian Academy of Sciences, Arbuzov Street 8, Kazan 420088, Russian Federation
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Publikationsverlauf

Received 21 May 2008
Publikationsdatum:
21. August 2008 (online)

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Abstract

Direct anodic oxidation of 2,4-dimethylphenol yields an unusual spiropentacyclic scaffold. An intermediate was isolated and structurally elucidated which strongly supports the postulated mechanism for the stereoselective formation of this spirolactone moiety. Additionally, we report an ameliorated protocol for the rearrangement to the spirolactone system.

Key words

phenol - spiro compounds - lactones - diastereoselectivity - rearrangements

    References and Notes

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Anodic Preparation of 5 2,4-Dimethylphenol (1, 24.4 g, 0.2 mol) was mixed with 0.1 M Ba(OH)2˙8H2O in MeOH (100 mL) and transferred into a nondivided standard electrolysis cell equipped with two platinum sheets as anode and cathode, respectively. At 25 ˚C a galvanostatic electrolysis with a current density of 12.5 mA/cm² was performed. During the electrolysis vigorous stirring is necessary and the formation of 5 as a light brown precipitate can be observed. After application of 33200 C (1.7 F/1) the precipitate was filtered off and washed with MeOH (40 mL) to yield analytically pure 5 (12.7 g, 26.34 mmol, 52%) as colorless solid; mp 146-148 ˚C. ¹H NMR (400 MHz, CDCl3): δ = 1.12 (s, 3 H), 1.53 (s, 3 H), 1.94 (d, J = 3 Hz, 3 H), 2.04 (s, 3 H), 2.20 (s, 3 H), 2.24 (s, 3 H), 2.29 (s, 3 H), 2.30 (s, 3 H), 5.05 (d, J = 2.16 Hz, 1 H), 5.17 (s, 1 H), 5.71 (s, 1 H), 6.08 (s, 1 H), 6.73 (d, J = 2.16 Hz, 1 H), 6.78 (s, 1 H), 6.85 (s, 1 H), 6.88 (dd, J = 8.19, 2.16 Hz, 1 H), 7.30 (d, J = 8.19 Hz, 1 H) ppm. ¹³C (100 MHz, CDCl3): δ = 15.03, 15.20, 15.34, 16.69, 20.63, 20.72, 20.85, 23.82, 46.80, 83.12, 84.66, 107.59, 119.63, 120.07, 120.28, 122.99, 123.67, 123.68, 126.89, 128.57, 128.96, 129.06, 130.47, 130.50, 131.28, 133.31, 133.74, 134.02, 134.43, 148.59, 156.74, 154.39 ppm. MS (EI, 70 eV): m/z (%) = 482.3 (34) [M]+ , 361.3 (100), 391.3 (33), 201.2 (76).

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CCDC 686744 (5) and CCDC 686745 (7), respectively, contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 (1223)336033, e-mail: deposit@ccdc.cam.ac.uk].