Synthesis of JKLM Ring Fragment of Ciguatoxin via Acetylene-Cobalt Strategy

Takayuki Baba; Minoru Isobe

doi:10.1055/s-2003-37533

LETTER

Synthesis of JKLM Ring Fragment of Ciguatoxin via Acetylene-Cobalt Strategy

Takayuki Baba, Minoru Isobe*
Laboratory of Organic Chemistry, School of Bioagricultural Sciences, Nagoya University Chikusa, Nagoya 464-8601, Japan
Fax: +81(52)7894111; e-Mail: isobem@agr.nagoya-u.ac.jp;

Abstract

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Abstract

A stereoselective synthesis of the JKLM ring fragment has been achieved through a coupling between two segments via heteroconjugate addition, seven-membered ether ring formation mediated by an acetylene cobalt complex and spiroketalization reaction.

Key words

acetylene cobalt complex - reductive decomplexation - heteroconjugate addition - medium sized ring - ciguatoxin

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References

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Physical data for 26. IR (KBr) 3447, 2926, 1717, 1636, 1456, 1355, 1077, 1025, 938, 739, 698, 419 cm^-1. ¹H NMR (CDCl₃, 400 MHz) d 1.01 (3 H, d, J = 6.5 Hz, CH ₃-60), 1.06 (3 H, d, J = 6.5 Hz, CH ₃-59), 1.12 (3 H, d, J = 7.5 Hz, CH ₃-58), 1.40 (1 H, q, J = 11.5 Hz, H-43a), 1.48 (1 H, dq, J = 11.0 Hz, 6.5 Hz, H-51), 1.61 (1 H, ddq, J = 11.0 Hz, 10.0 Hz, 6.5 Hz, H-50), 2.00 (1 H, qdd, J = 7.5 Hz, 5.0 Hz, 3.5 Hz, H-46), 2.08 (1 H, dd, J = 14.0 Hz, 4.0 Hz, H-53a), 2.13 (1 H, dd, J = 14.0 Hz, 6.5 Hz, H-53b), 2.45 (1 H, dd, J = 15.5 Hz, 9.0 Hz, H-40a), 2.54 (1 H, dt, J = 12.0 Hz, 4.5 Hz, H-43), 2.79 (1 H, dd, J = 15.5 Hz, 3.5 Hz, H-40b), 1.61 (1 H, ddq, J = 11.0 Hz, 10.0 Hz, 6.5 Hz, H-50), 2.95 (1 H, dd, J = 9.5 Hz, 5.0 Hz, H-45), 3.15 (1 H, ddd, J = 11.5 Hz, 9.0 Hz, 4.5 Hz, H-42), 3.26 (1 H, t, J = 9.5 Hz, H-49), 3.59 (1 H, td, J = 9.0 Hz, 3.5 Hz, H-41), 3.62 (1 H, dd, J = 9.5 Hz, 2.0 Hz, H-48), 3.65 (1 H, dd, J = 3.5 Hz, 2.0 Hz, H-47), 3.69 (1 H, ddd, J = 11.5 Hz, 9.5 Hz, 4.5 Hz, H-44), 3.85 (1 H, dd, J = 9.5 Hz, 5.0 Hz, H-55a), 3.96 (1 H, dd, J = 9.5 Hz, 2.0 Hz, H-55b), 4.26 (1 H, dddd, J = 6.5 Hz, 5.0 Hz, 4.0 Hz, 2.0 Hz, H-54), 4.39 (2 H, d, J = 11.5 Hz, -OCH ₂Ph), 4.45 (2 H, d, J = 12.0 Hz,
-OCH ₂Ph), 4.47 (2 H, d, J = 12.0 Hz, -OCH ₂Ph), 4.63 (2 H, d, J = 11.5 Hz, -OCH ₂Ph), 7.20-7,37 (10 H, m, aromatic). ESI Q-TOF MS calcd for C₃₅H₄₇O₈ 595.327 [M + H]⁺, found 595.336.