Synlett 2008(17): 2621-2624  
DOI: 10.1055/s-0028-1083513
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of a Bicyclo[8.3.1]enediyne via Chromium-Mediated Dearomatization of 2,6-Bis(trimethylsilyl)anisole

Séverine Lavy, Alejandro Pérez-Luna, E. Peter Kündig*
Department of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211 Geneva 4, Switzerland
Fax: +41(22)3793215; e-Mail: Peter.Kundig@chiorg.unige.ch;
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Publikationsverlauf

Received 18 July 2008
Publikationsdatum:
01. Oktober 2008 (online)

Abstract

A novel bicyclo[8.3.1]enediyne was readily synthesized by chromium-mediated dearomatization of 2,6-bis(trimethyl­silyl)anisole. The enediyne undergoes Bergman cyclization with a half-life of 14.4 hours at 142 ˚C.

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Spectroscopic Data
Compound rac -4: ¹H NMR (400 MHz, C6D6): δ = 0.18 (d, J = 4.8 Hz, 6 H), 0.29 (s, 9 H), 0.98 (s, 9 H), 1.80 (t, J = 2.8 Hz, 1 H), 2.10 (m, 1 H), 2.25 (m, 2 H), 3.02 (dt, J = 8.8, 4.0 Hz, 1 H), 4.75 (d, J = 4.3 Hz, 1 H), 4.94 (dd, J = 10.1, 1.8 Hz, 1 H), 5.06 (d, J = 16.4 Hz, 1 H), 5.66 (ddd, J = 16.9, 9.8, 8.1 Hz, 1 H), 6.27 (d, J = 3.3 Hz, 1 H). ¹³C NMR (100 MHz, C6D6): δ = -3.8, -0.3, 18.9, 21.8, 26.6, 39.4, 43.6, 70.7, 82.7, 101.7, 115.1, 128.1, 138.4, 141.1, 152.4. IR: 3403, 2930, 2280, 1730, 1720, 1618, 1593, 1456, 1424, 1330, 1230, 4458, 1056, 1025, 768, 741 cm. MS: 347, 273, 249, 231, 217, 195, 163. HRMS: m/z calcd for C20H35OSi2: 347.2226; found: 347.2230.
Compound rac -6: ¹H NMR (400 MHz, C6D6): δ = 0.19 (dd, J = 5.0, 1.8 Hz, 6 H), 0.29 (s, 9 H), 0.98 (s, 9 H), 2.40 (m,
3 H), 3.16 (m, 1 H), 4.08 (s, 2 H), 4.79 (m, 1 H), 4.95 (d, J = 10.1 Hz, 1 H), 5.13 (d, J = 17.2 Hz, 1 H), 5.54 (m, 2 H), 5.70 (m, 1 H), 6.26 (bs, 1 H). ¹³C NMR (100 MHz, C6D6):
δ = -3.8, -0.3, 12.3, 18.9, 23.1, 26.6, 39.7, 43.4, 46.7, 51.6, 80.8, 83.3, 95.5, 97.2, 101.7, 115.2, 118.5, 120.6, 128.7, 138.5, 141.2, 141.3, 152.5. IR: 3420, 2954, 2928, 2214, 1623, 1572, 1473, 1407, 1361, 1330, 1245, 1203, 835 cm. MS: 427, 355, 338, 279, 241. HRMS: m/z calcd for C25H39O2Si2: 427.2483; found: 427.2501.
Compound rac -8: ¹H NMR (400 MHz, C6D6): δ = 0.24 (s, 9 H), 2.02 (m, 1 H), 2.15 (m, 1 H), 2.30 (m, 1 H), 2.74 (m,
1 H), 3.48 (m, 2 H), 3.52 (m, 1 H), 4.90 (m, 2 H), 5.28 (dt, J = 9.6, 2.8 Hz, 1 H), 5.66 (ddd, J = 17.1, 10.6, 6.6 Hz, 1 H), 6.29 (d, J = 9.9 Hz, 1 H), 6.55 (d, J = 5.3 Hz, 1 H). ¹³C NMR (100 MHz, C6D6): δ = -1.3, 26.3, 38.6, 39.5, 39.7, 52.0 109.5, 115.0, 140.1, 141.6. IR: 3585, 2953, 2089, 2050, 2016, 1639, 1601, 1426, 1316, 1277, 1246, 910, 835, 784, 760 cm. MS: m/z = 598 [M + NH4 +], 581, 356, 339, 300. HRMS: m/z calcd for C25H23O7SiCo2 [M + H+]: 580.9877; found: 580.9859.
Compound rac -2: ¹H NMR (400 MHz, C6D6): δ = 0.33 (s, 9 H), 1.96 (m, 3 H), 2.35 (dd, J = 16.9, 4.3 Hz, 1 H), 2.53 (dd, J = 17.2, 4.5 Hz, 1 H), 3.21 (ddd, J = 16.9, 3.3, 2.0 Hz, 1 H), 4.12 (q, J = 8.8 Hz, 1 H), 4.84 (m, 2 H), 5.29 (m, 3 H), 6.49 (d, J = 2.8, 1 H). ¹³C NMR (100 MHz, C6D6): δ = -1.1, 23.5, 25.9, 38.2, 42.8, 46.7, 83.4, 84.2, 95.8, 97.7, 116.5, 120.8, 122.3, 140.7, 143.7, 158.3, 200,1. IR: 2280, 1656, 1611, 1450, 1328, 822 cm. MS: m/z = 295, 279, 203, 190. HRMS: m/z calcd for C19H22OSiNa [M + Na]: 317.1335; found : 317.1335.
Compound rac -9: ¹H NMR (400 MHz, C6D6): δ = -0.01 (s, 9 H), 2.39 (m, 2 H), 2.69 (m, 4 H), 2.99 (dd, J = 14.3, 7.5 Hz 1 H), 4.91 (m, 2 H), 5.85 (ddd, J = 17.3,10.5, 6.4 Hz, 1 H), 6.33 (dd, J = 5.7, 1.5 Hz, 1 H), 6.68 (m, 1 H), 6.90 (m, 3 H). ¹³C NMR (100 MHz, C6D6): δ = -1.5, 38.0, 41.0, 41.2, 47.7, 53.2, 114.8, 126.9, 128.6, 129.6, 131.2, 141.7, 156.0. IR: 2921, 1651, 1589, 1491, 1456, 1348, 1338, 1241, 1218, 1124, 985, 918, 856, 834, 744 cm. MS: m/z = 297, 283, 282. HRMS: m/z calcd for C19H24NaOSi: 319.1488; found: 319.1491.

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SPARTAN’02, Wavefunction, Inc., Irvine, CA;
http://www.wavefun.com.

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A solution of 2 (50.1 mg, 0.17 mmol) and pyrene (9 mg, 0.04 mmol) in 1,4-cyclohexadiene (5 mL) under N2 was heated in a sealed tube. After the appropriate reaction time the sealed tube was cooled in H2O and opened. An aliquot of 100 µL was removed and brought to dryness in vacuo. The solid residue was taken up in pentane (1 mL) and then analyzed by HPLC [column: SiO2 SPHERI5, solvent: hexane-i-PrOH (99:1); flow rate: 1 mL/min, detector: UV, λ = 245; sample loop: 5 µL]. The concentration of 2 and 9 was determined as the area ratio of the peaks corresponding to 2, 9, and the internal standard.