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Synlett 2005(4): 703-705  
DOI: 10.1055/s-2005-863703
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© Georg Thieme Verlag Stuttgart · New York

Biomimetic Tandem Cyclization Catalyzed by Hg(OTf)2 Affording ­Polycarbocycles

Hiroshi Imagawa, Tomoaki Iyenaga, Mugio Nishizawa*
Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514, Japan
Fax: +81(88)6553051; e-Mail: mugi@ph.bunri-u.ac.jp;
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Publication History

Received 22 October 2004
Publication Date:
22 February 2005 (online)

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Abstract

Efficient biomimetic tandem cyclization catalyzed by Hg(OTf)2 was achieved to give tricyclic 4 and tetractyclic 6 in high catalytic turnover. Structures of cyclization products were confirmed by X-ray diffraction study.

Key words

biomimetic - cyclization - alkyne - mercuric triflate - catalysis

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Spectroscopic data for 4: 1H NMR (200 MHz, CDCl3): δ = 1.03 (s, 3 H), 1.30 (d, J = 6.8 Hz, 3 H), 1.31 (d, J = 6.8 Hz, 3 H), 1.48-1.71 (m, 2 H), 2.06-2.30 (m, 4 H), 2.75-3.03 (m, 2 H), 3.30 (sept., J = 6.8 Hz, 1 H), 3.78 (s, 3 H), 5.42 (br s, 1 H), 6.73 (d, J = 8.8 Hz, 1 H), 7.18 (d, J = 8.8 Hz, 1 H).
13C NMR (50 MHz, CDCl3): δ = 20.30 (q), 20.33 (q), 20.89 (t), 21.32 (q), 22.57 (q), 23.39 (t), 27.41 (t), 34.24 (t), 35.81 (s), 43.30 (d), 54.97 (q), 109.14 (d), 121.44 (d), 122.50 (d), 133.92 (s), 134.88 (s), 134.88 (s), 140.10 (s), 156.78 (s).
FT-IR: 2955, 2836, 1589, 1480, 1454, 1260, 1119, 1051, 802 cm-1. MS (EI): m/z = 284 [M+]. HRMS (EI): m/z calcd for C20H28O [M+]: 284.2140; found: 284.2136. Crystal data: C20H28O, colorless cube, crystal dimension 0.4 × 0.3 × 0.2 mm, M r = 284.443, monoclinic P21/n, a = 8.165 (6)Å, b = 21.156 (2) Å, c = 9.8190 (12) Å, β = 94.919 (3)°, V = 1689.9 (3) Å3, Z = 4, ρcalcd = 1.118 mg m-3, µ = 0.066 mm-1, T = 298 K, 2794 measured reflections, 2752 independent reflections, 190 parameters, GOF = 1.031, R1 (wR2) = 0.0624 (0.1905).

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Spectroscopic data for 6: 1H NMR (600 MHz, CDCl3): δ = 1.12 (ddd, J = 7.4, 12.0, 12.0 Hz, 1 H), 1.25 (d, J = 10.8 Hz, 1 H), 1.28 (m, 1 H), 1.32 (s, 3 H), 1.49 (dt, J = 3.0, 13.8 Hz, 1 H), 1.53-1.61 (m, 1 H), 1.75 (dq, J = 3.6, 13.8 Hz, 1 H), 1.84-1.95 (m, 3 H), 2.02 (m, 1 H), 2.09 (m, 1 H), 2.84 (m, 2 H), 3.20 (dt, J = 3.0, 13.2 Hz, 1 H), 3.76 (d, J = 2.5 Hz, 1 H), 5.28 (br s, 1 H), 6.20 (d, J = 2.7 Hz, 1 H), 6.28 (d, J = 2.7 Hz, 1 H). 13C NMR (50 MHz, CDCl3): δ = 12.79 (q), 18.15 (t), 21.10 (q), 21.41 (t), 21.49 (q), 23.03 (t), 33.56 (t), 35.64 (t), 36.28 (s), 37.90 (t), 39.47 (s), 48.81 (d), 54.76 (d), 55.06 (q), 55.09 (q), 97.65 (d), 104.85 (d), 120.13 (d), 130.68 (s), 135.18 (s), 138.78 (s), 157.80 (s), 159.60 (s). FT-IR: 2933, 1604, 1579, 1454, 1271, 1206, 1153, 825 cm-1. MS (EI): m/z = 340 [M+]. HRMS (EI): m/z calcd for C23H32O2 [M+]: 340.2402; found: 340.2396. Crystal data: C23H32O2, colorless plate, crystal dimension 0.40 × 0.35 × 0.10 mm, M r = 340.507, triclinic P1, a = 6.797 (2)Å, b = 7.517 (2) Å, c = 21.214 (6) Å, α = 84.62 (2)°, β = 85.53 (2)°, γ = 61.406 (14)°, V = 946.8 (5) Å3, Z = 2, ρcalcd = 1.194 mg m-3, µ = 0.074 mm-1, T = 298 K, 2950 measured reflections, 2950 independent reflections, 226 parameters, GOF = 1.053, R1 (wR2) = 0.0850 (0.2229).

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The measurements were carried out on Mac Science (Bruker Nonius) dip image plate diffractometer using graphite-monochromated MoKα radiation (λ = 0.71073 Å). The crystal structure was solved by the direct method with SIR-97. Refinement was performed by a full matrix least squares refinement on F2 with SHELXL-97. CCDC 253197 (4) and CCDC 253198 (6) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK; fax: +44 (1223)336033; or deposit@ccdc.cam.ac.uk].