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

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.

enediynes - dearomatization - [Cr(arene)(CO)₃] complexes - Bergman cyclization - Nicholas reaction

References and Notes

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14

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^-¹. 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^-¹. 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^-¹. 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^-¹. 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^-¹. MS: m/z = 297, 283, 282. HRMS: m/z calcd for C₁₉H₂₄NaOSi: 319.1488; found: 319.1491.

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17

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

18

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.

19 O’Connor JM. Friese SJ. Rodgers BL. J. Am. Chem. Soc.  2005,  127:  16342 ; and references cited therein