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Synlett 2006(16): 2617-2620  
DOI: 10.1055/s-2006-951476
LETTER
© Georg Thieme Verlag Stuttgart · New York

CaCl2- or MgCl2 -Catalyzed Allylic Oxidations of Ionone-like Dienes

Min Yanga,c, Qian-Rong Pengb, Jing-Bo Lana, Guang-Fu Songc, Ru-Gang Xie*a
a Department of Chemistry, Sichuan University, Chengdu, 610064, P. R. of China
Fax: +86(28)85411684; e-Mail: orgxie@scu.edu.cn; e-Mail: schemorg@mail.sc.cninfo.net;
b Technology Center, Guizhou Huang Guo Shu Tobacco Group, Guiyang, 550003, P. R. of China
c Department of Chemistry Technology, Guizhou University, Guiyang, 550003, P. R. of China
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Publication History

Received 16 April 2006
Publication Date:
22 September 2006 (online)

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Abstract

The allylic oxidation of ionone-like dienes catalyzed by CaCl2 or MgCl2 with TBHP is presented. The method provides a facile method to synthesize dienones derived from ionone-like dienes in good to moderate yields. A plausible mechanism for the oxidation is proposed.

Key words

allylic oxidation - ionone-like dienes - calcium chloride - magnesium chloride - tert-butyl hydroperoxide

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Allylic Oxidation of Ionone-Like Dienes; Typical Procedure: To a mixture of ionone-like diene 1 (1 mmol) and CaCl2 or MgCl2·6H2O (0.2 mmol) in MeCN (6 mL) was addded aq TBHP (70%, 3-5 mmol) in one or two portions under vigorous stirring at 60 °C for 1-5 h. The resulting mixture was concentrated under reduced pressure to give a residue (0.5 mL), which was purified by column chromatog-raphy on silica gel (PE-EtOAc, 3:1) to give dienone 2 and small amounts of 5,6-β-epoxides. Alternatively, the product could be isolated by distillation under reduced pressure, particularly when the reaction was performed on >5 mmol scale. Analytical data for compounds 2a, 2b, 2d, and 2e is consistent with those previously reported. [5a] [c] [f] Compound 2c: 1H NMR (400 MHz, CDCl3): δ = 5.92 (br s, 1 H), 5.46-5.49 (m, 1 H), 5.46-5.49 (m, 1 H), 3.81-3.85 (m, 1 H), 3.29-3.50 (m, 2 H), 2.50-2.53 (m, 1 H), 2.31 (d, J = 16.8 Hz, 1 H), 2.06 (d, J = 16.8 Hz, 1 H), 1.88 (d, J = 1.2 Hz, 3 H), 1.22 (d, J = 4 Hz, 3 H), 1.16 (t, J = 5.4 Hz, 3 H), 1.01 (s, 3 H), 0.98 (s, 3 H). 13C NMR (400 MHz): δ = 198.75, 161.49, 137.07, 127.98, 125.69, 63.44, 55.46, 47.44, 35.88, 29.48, 27.27, 26.94, 23.45, 21.68, 15.22. HRMS (ESI): m/z calcd for C15H24O2 [M + Na]+: 259.1674; found: 259.1669.Compound 2f: 1H NMR (400 MHz, CDCl3): δ = 6.16 (d, J = 16.0 Hz, 1 H), 5.55 (q, J = 16.4 Hz, 1 H), 3.93-3.99 (m, 1 H), 3.40-3.60 (m, 2 H), 2.50 (t, J = 7.0 Hz, 2 H), 1.85 (t, J = 6.8 Hz, 2 H), 1.81 (s, 3 H), 1.31 (d, J = 6.8 Hz, 3 H), 1.23 (t, J = 7.2 Hz, 3 H), 1.16 (s, 3 H), 1.15 (s, 3 H). 13C NMR (200 MHz): δ = 199.26, 160.45, 139.02, 129.92, 126.77, 63.68, 37.17, 35.33, 34.22, 27.27, 27.27, 26.50, 21.77, 15.36, 13.31. HRMS (ESI): m/z calcd for C15H24O2 [M + Na]+: 259.1674; found: 259.1674.