Construction of Cyclohepta[b]indoles via Platinum-Catalyzed Intermolecular Formal [4+3]-Cycloaddition Reaction of α,β-Unsaturated Carbene Complex Intermediates with Siloxydienes

Abstract

Platinum(II)-catalyzed intermolecular formal [4+3]-cycloaddition reaction of α,β-unsaturated carbene complex intermediates with siloxydienes proceeded under mild conditions to give cyclohepta[b]indole derivatives in good yield. The reaction was found to proceed via 1,2-alkyl shift of the carbene complex intermediates obtained by [4+2]-cycloaddition reaction of the unsaturated carbenes with dienes.

Key words

platinum - alkynes - cycloaddition - siloxy diene - cyclohepta[b]indole

• References and Notes

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• 22 Selected Compound Data Compound 6a: colorless oil. IR (neat): 3049, 2944, 2867, 1730, 1667, 1458, 1369, 1355, 1149, 1119, 742, 683 cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 0.95 (t, J = 7.3 Hz, 3 H), 1.09–1.13 (m, 18 H), 1.15–1.25 (m, 3 H), 1.38–1.48 (m, 1 H), 1.48–1.57 (m, 1 H), 1.69 (s, 9 H), 1.70–1.79 (m, 2 H), 2.40 (ddd, J = 3.2, 8.2, 15.4 Hz, 1 H), 2.78 (ddd, J = 2.9, 10.3, 15.4 Hz, 1 H), 3.20 (ddd, J = 2.9, 8.2, 16.9 Hz, 1 H), 3.44–3.53 (m, 2 H), 5.24 (d, J = 8.1 Hz, 1 H), 7.19–7.25 (m, 2 H), 7.38–7.42 (m, 1 H), 8.02–8.07 (m, 1 H). ¹³C NMR (125 MHz in CDCl₃): δ = 12.6, 14.2, 18.04, 18.05, 21.7, 25.3, 28.3, 32.2, 32.4, 39.2, 83.5, 107.4, 115.2, 117.5, 121.7, 122.2, 123.2, 130.2, 135.1, 136.6, 150.8, 153.1. HRMS–FAB: m/z [M]⁺ calcd for C₃₀H₄₇NO₃Si: 497.3325; found: 497.3346. Compound 7a: colorless oil. IR (neat): 3048, 2944, 2867, 1709, 1656, 1478, 1368, 1347, 1224, 1178, 883, 749, 684 cm^–1. ¹H NMR (500 MHz, CDCl₃, 330 K): δ = 0.72 (t, J = 7.4 Hz, 3 H), 0.94–0.99 (m, 2 H), 1.11–1.15 (m, 18 H), 1.15–1.25 (m, 3 H), 1.25–1.44 (m, 2 H), 1.58 (s, 9 H), 2.12–2.20 (m, 2 H), 2.23–2.31 (m, 1 H), 2.47 (s, 1 H), 2.90–3.04 (m, 1 H), 5.16 (s, 1 H), 6.91 (dt, J = 0.9, 7.4 Hz, 1 H), 7.10–7.15 (m, 2 H), 7.68–7.75 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃, 330 K): δ = 12.8, 14.1, 18.0, 19.8, 24.8, 25.8, 27.8, 28.5, 28.9, 39.7, 55.3, 81.3, 107.3, 115.0, 122.3, 124.6, 126.7, 130.1, 145.9, 150.5, 153.2. HRMS–FAB: m/z [M]⁺ calcd for C₃₀H₄₇NO₃Si: 497.3325; found: 497.3329. Compound 6h: colorless oil. IR (neat): 3050, 2942, 2866, 1730, 1655, 1456, 1357, 1132, 1117, 883, 743, 687 cm^–1. ¹H NMR (500 MHz in CDCl₃): δ = 1.06–1.10 (m, 18 H), 1.13–1.23 (m, 3 H), 1.66 (s, 9 H), 1.81–1.93 (m, 2 H), 2.03–2.13 (m, 2 H), 2.76–2.80 (m, 1 H), 3.10 (dd, J = 4.6, 18.2 Hz, 1 H), 3.44 (br d, J = 18.2 Hz, 1 H), 3.53–3.57 (m, 1 H), 5.53 (dd, J = 1.8, 7.9 Hz, 1 H), 7.18–7.22 (m, 2 H), 7.42–7.47 (m, 1 H), 8.05–8.10 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 12.6, 17.97, 17.99, 25.9, 28.2, 28.3, 31.7, 35.6, 37.8, 83.3, 109.4, 115.4, 116.9, 122.1, 123.0, 123.4, 128.8, 133.9, 134.9, 150.7, 154.0. HRMS–FAB: m/z [M]⁺ calcd for C₂₉H₄₃NO₃Si: 481.3012; found: 481.3021. Compound 9: pale yellow oil. IR (neat): 3046, 2945, 2866, 1663, 1598, 1452, 1381, 1367, 1173, 746, 684 cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 0.75 (d, J = 6.8 Hz, 3 H), 0.89 (d, J = 6.6 Hz, 3 H), 1.02–1.07 (m, 18 H), 1.08–1.18 (m, 3 H), 1.90–2.00 (m, 1 H), 2.06–2.16 (m, 1 H), 2.32 (s, 3 H), 2.41 (ddd, J = 3.2, 6.4, 16.8 Hz, 1 H), 3.11 (ddd, J = 3.2, 11.7, 16.1 Hz, 1 H), 3.23 (t, J = 7.4 Hz, 1 H), 3.64 (ddd, J = 3.5, 6.4, 16.1 Hz, 1 H), 5.12 (dd, J = 0.7, 7.4 Hz, 1 H), 7.14 (d, J = 8.2 Hz, 2 H), 7.21–7.29 (m, 2 H), 7.33–7.36 (m, 1 H), 7.51–7.55 (m, 2 H), 8.22–8.26 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 12.6, 17.97, 17.99, 20.5, 21.5, 21.7, 22.8, 31.7, 35.2, 39.7, 105.9, 115.4, 118.3, 123.3, 123.8, 124.3, 126.1, 129.6, 131.4, 136.1, 136.3, 136.4, 144.5, 152.0. HRMS–FAB: m/z [M]⁺ calcd for C₃₂H₄₅NO₃SSi: 551.2889; found: 551.2881.