Synlett 2011(5): 722-724  
DOI: 10.1055/s-0030-1259677
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthetic Studies toward the Total Synthesis of Chlorahololide A

Shan Qian, Gang Zhao*
Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Rd., Shanghai 200032, P. R. of China
Fax: +86(21)64166128; e-Mail: zhaog@mail.sioc.ac.cn;
Further Information

Publication History

Received 25 December 2010
Publication Date:
22 February 2011 (online)

Abstract

The highly stereoselective synthesis of core framework 4, a pivotal intermediate for the total synthesis of chlorahololide A, is reported. The approach features t-BuCu-mediated stereoselective reduction of α,β-unsaturated diketone 8, Wharton transposition, Simmons-Smith cyclopropanation and cascade enol lactonization.

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The same operative procedure should be conducted to ensure that the starting material is completely consumed. For details, see the Supporting Information.

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See the Supporting Information for details. CCDC 804060 (4) and 804061 (14) contain the supplementary crystallogra-phic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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Data of the Core Fragment 4
[α]D ²8 56.2 (c 0.12, CHCl3); mp 133-135 ˚C. IR (film): 2921, 2850, 1735, 1464, 1374, 1265, 1045 cm. ¹H NMR (400 MHz, CDCl3): δ = 6.16 (s, 1 H), 4.39 (t, J = 5.2 Hz, 1 H), 2.60-2.40 (m, 2 H), 2.20-2.10 (m, 1 H), 1.89 (s, 3 H), 1.80-1.65 (m, 1 H), 1.65-1.50 (m, 1 H), 1.30-1.20 (m, 1 H), 1.09 (s, 3 H), 0.91 (s, 9 H), 1.80-1.65 (m, 1 H), 0.10 (s, 3 H), 0.07 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 171.2, 149.4, 149.3, 122.1, 121.0, 72.9, 61.9, 42.1, 29.1, 26.2, 25.8, 23.3, 21.4, 18.2, 12.1, 8.5, -4.7, -5.3. ESI-MS: m/z = 369.2 [M + Na]+. ESI-HRMS: m/z calcd for C20H30O3SiNa+ [M + Na]+: 369.1862; found: 369.1856.