First Thermal and Transition Metal Catalysed Intramolecular [4+2] Cycloaddition Reactions with N-Tethered Ynamides

Abstract

Cationic rhodium(I)-complexes generated from [RhCl(PPh₃)₃] and AgSbF₆ catalyse at room temperature the first examples of intramolecular [4+2] cycloaddition reactions with N-tethered ynamides and provide an efficient access to synthetically versatile tetrahydroindoles.

ynamides - tetrahydroindoles - Diels-Alder reaction - catalysis - alkynyliodonium salts

References

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Spectral data for dienyne 7: ¹H NMR (400 MHz, CDCl₃): δ = 7.80 (m, 2 H), 7.35 (m, 2 H), 6.23 (m, 1 H), 6.07 (m, 1 H), 5.55 (m, 1 H), 5.11 (d, J = 16.1 Hz, 1 H), 5.01 (d, J = 9.1 Hz, 1 H), 3.38 (m, 2 H), 2.78 (s, 1 H), 2.43 (s, 3 H), 2.39 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 144.7, 136.6, 133.8, 130.0, 129.8, 127.6, 134.6, 116.3, 75.8, 59.5, 50.6, 30.9, 21.6.

Nickel(0)-catalysed intramolecular [4+2] cycloaddition reactions:

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Rhodium(I)- and cationic rhodium(I)-catalysed intramolecular [4+2] cycloaddition reactions:

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<A NAME="RG00203ST-11">11</A>

Experimental Procedure: [RhCl(PPh₃)₃] (9.3 mg, 0.01 mmol) was added to a solution of ynamide 4-8 (0.20 mmol) in dry toluene (10 mL) under argon. After stirring for 5 min at r.t., AgSbF₆ (0.01 mmol, 0.2 mL of a 0.05 M solution in 1,2-dichloroethane) was added and the reaction mixture was stirred at r.t. The reaction mixture was filtered through a small plug of celite, the solvent was evaporated and the resulting crude product was purified by column chromatography (Al₂O₃ III/N, hexanes-EtOAc = 8:2) to afford 9, 11-14.
Compound 9: Mp 87-88 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.72 (d, J = 8.4 Hz, 2 H), 7.28 (d, J = 8.4 Hz, 2 H), 5.76 (m, 2 H), 5.66 (m, 1 H), 3.76 (m, 1 H), 3.33 (m, 1 H), 2.77 (m, 2 H), 2.54 (m, 1 H), 2.41 (s, 3 H), 2.02 (m, 1 H), 1.49 (m, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 143.6, 137.9, 134.8, 129.5, 127.2, 126.5, 125.3, 103.1, 48.9, 38.0, 28.7, 26.9, 21.5. MS (EI, 70 eV): m/z (%) = 275 (43) [M⁺], 91 (100). Anal. Calcd for C₁₅H₁₇NO₂S: C, 65.43; H, 6.22; N, 5.09. Found: C, 65.15; H, 6.06; N, 5.31. Compound 11: Mp 74-75 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.70 (d, J = 8.3 Hz, 2 H), 7.27 (d, J = 8.3 Hz, 2 H), 5.79 (m, 1 H), 5.64 (m, 1 H), 3.46 (m, 2 H), 2.96-2.81 (m, 2 H), 2.47 (s, 3 H), 1.89 (m, 2 H), 1.34 (m, 1 H), 0.35 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 145.2, 143.6, 134.8, 129.5, 128.1, 125.9, 125.8, 125.7, 47.2, 36.9, 29.8, 28.7, 21.5, 0.0. MS (EI, 70 eV): m/z (%) = 347 (3) [M⁺], 99 (100). Anal. Calcd for C₁₈H₂₅NO₂SSi: C, 62.21; H, 7.25; N, 4.03. Found: C, 61.98; H, 7.35; N, 3.93. Compound 13: Mp 121-122 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.52 (m, 2 H), 7.44 (m, 2 H), 7.32 (m, 2 H), 7.22 (m, 3 H), 5.77 (m, 1 H), 5.70 (m, 1 H), 3.54 (m, 2 H), 3.38 (m, 1 H), 2.78 (m, 1 H), 2.40 (s, 3 H), 2.23 (m, 1 H), 2.11 (m, 1 H), 1.55 (m, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 143.4, 141.0, 134.1, 129.4, 128.0, 127.6, 125.4, 125.3, 124.8, 47.7, 38.0, 33.3, 29.3, 21.6. Compound 14: Oil. ¹H NMR (400 MHz, CDCl₃) δ = 7.67 (d, J = 8.2 Hz, 2 H), 7.27 (d, J = 8.2 Hz, 2 H), 5.67 (m, 1 H), 5.54 (m, 1 H), 3.42 (m, 2 H), 2.89 (m, 1 H), 2.60 (m, 2 H), 2.41 (s, 3 H), 2.34 (m, 1 H), 1.87 (m, 2 H), 1.52 (m, 1 H), 1.38 (m, 3 H), 1.28 (m, 1 H), 0.93 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃) δ = 143.5, 134.6, 131.8, 129.5, 128.5, 127.8, 125.7, 124.8, 47.9, 36.8, 32.0, 31.0, 29.6, 29.4, 22.9, 21.5, 14.0.

<A NAME="RG00203ST-12">12</A>

Crystal data for 12: C₁₃H₁₈NOF₃Si, triclinic, space group
P1 (No. 2), a = 8.896 (2), b = 9.643 (2), c = 9.830 (2) Å, α = 102.38 (3)°, β = 115.97 (3)°, γ = 92.73 (3)°, V = 730.8 (3) ų, Z = 2, D _c = 1.315 g cm^-3, F ₍₀₀₀₎ = 304,
µ (Mo-Kα) = 1.85 cm^-1. 6235 reflections collected, 2650 independent [R(int) = 0.0449], which were used in all calculations. 172 parameters, R ₁ = 0.0457, wR ₂ = 0.1129 for observed reflections [F²>2σ(F²)] and R ₁ = 0.0597, wR ₂ = 0.1217 for all reflections, GoF (on F²) = 0.871. Max. and min. residual electron densities: 0.285 and -0.231 eÅ^-3. Data were collected on a STOE-IPDS at r.t., the structure was solved by direct methods using SHELXS-97 and refined using SHELXL-97. CCDC: 194177.