Construction of the AG-ring Unit of Pinnatoxin A via Intramolecular Alkylation and Aza-Wittig Reaction

Jin Wang; Satoshi Sakamoto; Kei Kamada; Aiko Nitta; Takeshi Noda; Hiroki Oguri; Masahiro Hirama

doi:10.1055/s-2003-38752

LETTER

Construction of the AG-ring Unit of Pinnatoxin A via Intramolecular Alkylation and Aza-Wittig Reaction

Jin Wang, Satoshi Sakamoto, Kei Kamada, Aiko Nitta, Takeshi Noda, Hiroki Oguri, Masahiro Hirama*
Department of Chemistry, Graduate School of Science, Tohoku University, and CREST, Japan Science and Technology Corporation (JST), Sendai 980-8578, Japan
Fax: +81(22)2176566; e-Mail: hirama@ykbsc.chem.tohoku.ac.jp;

Abstract

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Abstract

An efficient synthetic route to the spirally fused AG-ring model of pinnatoxin A has been devised using the intramolecular cyclization of epoxy nitrile followed by an aza-Wittig reaction to form a seven-membered cyclic imine.

Key words

pinnatoxin A - cyclic imine - alkylation - spiro ring - aza-Wittig reaction

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References

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Physical data for 2: [α]_D ²⁹ +31 (c 0.096, CH₃OH); IR(film) 3369(br), 2955, 2927, 2871, 1681, 1666, 1567, 1557, 1456, 1433, 1380, 1370, 1348, 1248, 1223, 1202, 1162, 1134, 1068, 1042, 922, 861, 796, 737, 702, 665, 515 cm^-1; ¹H NMR (500 MHz, CD₃OD) 6.12 (1 H, br s, H32), 4.23 (1 H, dd, J = 3.8 Hz, 13.2 Hz, H1), 4.20 (1 H, dd, J = 5.3 Hz, 7.4 Hz, H29), 3.94 (1 H, m, H30), 3.83 (1 H, t, J = 8.0 Hz, H29), 3.44 (1 H, d, J = 13.2 Hz, H1), 3.28 (1 H, br d, H31), 2.66 (3 H, s, H7), 2.57 (1 H, br d, H35), 2.44 (1 H, br, H35), 1.99 (1 H, m, H39), 1.97 (1 H, d, J = 15.0 Hz, H4), 1.92 (1 H, m, H3), 1.82 (1 H, m, H39), 1.66 (1 H, m, H2), 1.64 (1 H, d, J = 14.6 Hz, H4), 1.46 (3 H, s, CH₃), 1.34 (3 H, s, CH₃), 1.14 (3 H, d, J = 7.0 Hz, H41), 1.06 (3 H, d, J = 6.5 Hz, H40); ¹³C NMR (125 MHz, CD₃OD) 200.49, 173.44, 129.91, 76.42, 70.47, 51.94, 49.82, 48.18, 40.05, 53.69, 33.95, 32.78, 22.66, 21.11, 18.70; MALDI-TOF MS calcd for C₂₀H₃₂NO₄ [M + H⁺] 350.233; found 350.323.