Synthesis of 1-Indol-3-yl-carbazoles via Garratt-Braverman Cyclization

Abstract

Various indolyl carbazoles have been prepared in good yields utilizing Garratt-Braverman cyclization of bisindolyl propargyl sulfones, ethers, and amines as the key step.

Key word

Garratt-Braverman cyclization - carbazole - indole - alkaloid - Sonogashira coupling - sulfone

References and Notes

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12

The indole nitrogen had to be protected due to the instability of 3-iodoindole under Pd(0)-catalyzed reaction conditions.

14

CCDC 848846 contains the crystallographic data for this paper.

15

All compounds were characterized by NMR and MS analysis.
Spectral Data of Selected Compounds
Compound 18a: ^¹H NMR (400 MHz, CDCl₃): δ = 8.30 (d, J = 8.0 Hz, 1 H), 8.08 (d, J = 8.4 Hz, 1 H), 8.03 (s, 1 H), 8.01 (s, 1 H), 7.64 (s, 1 H), 7.55-7.51 (m, 1 H), 7.44-7.41 (m, 1 H), 7.28-7.27 (2 H, m), 4.62 (s, 2 H), 4.57-4.52 (m, 2 H), 4.45, 4.31 (ABq, J = 16.0 Hz, 2 H), 3.75-3.69 (m, 1 H), 3.30-3.25 (m, 1 H), 1.49 (t, J = 5.2 Hz, 3 H), 0.75 (t, J = 7.2 Hz, 3 H). ^¹³C NMR (100 MHz, CDCl ₃): δ = 151.2, 150.6, 139.9, 137.5, 135.2, 130.6, 128.6, 128.1, 128.0, 126.5, 125.4, 124.3, 123.6, 123.5, 122.7, 119.9, 119.8, 119.6, 118.9, 116.9, 115.5, 114.8, 63.6, 63.2, 57.5, 57.4, 14.3, 13.4. HRMS: m/z calcd for C₂₈H₂₄N₂O₂S + H⁺: 517.1433; found: 517.1440.
Compound 21a: ^¹H NMR (400 MHz, CD₃COCD₃): δ = 10.7 (br s, 1 H), 10.0 (br s, 1 H), 8.16 (s, 1 H), 8.14 (s, 1 H), 7.67-7.66 (m, 1 H), 7.57 (d, J = 8.0 Hz, 1 H), 7.49 (d, J = 8.4 Hz, 1 H), 7.37 (t, J = 7.6 Hz, 1 H), 7.30 (d, J = 8.0 Hz, 1 H), 7.23-7.18 (m, 2 H), 7.07 (t, J = 7.6 Hz, 1 H), 4.64 (s, 2 H), 4.39, 4.33 (ABq, J = 16.0 Hz, 2 H). ^¹³C NMR (100 MHz, CD₃COCD₃): δ = 140.7, 139.3, 137.0, 129.0, 126.5, 126.2, 125.1, 123.3, 123.2, 123.1, 122.2, 120.4, 120.0, 119.5, 119.3, 116.8, 116.3, 112.1, 111.5, 110.2, 57.3, 56.7. HRMS: m/z calcd for C₂₂H₁₆N₂O₂S + H⁺: 373.1011; found: 373.1014.
Compound 18b: ^¹H NMR (400 MHz, CDCl₃): δ = 8.00 (s, 1 H), 7.90-7,88 (m, 1 H), 7.62 (s, 1 H), 7.27-7.18 (m, 4 H), 7.09 (d, J = 6.4 Hz, 1 H), 4.64, 4.58 (ABq, J = 15.6 Hz, 2 H), 4.50, 4.47 (ABq, J = 6.8 Hz, 2 H), 4.31, 4.14 (ABq, J = 16.4 Hz, 2 H), 3.71-3.63 (m, 1 H), 2.99-2.91 (m, 1 H), 2.72 (s, 3 H), 2.45 (s, 3 H), 1.46 (t, J = 6.8 Hz, 3 H), 0.73 (t, J = 7.2 Hz, 3 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 153.6, 150.5, 138.7, 138.5, 134.7, 130.5, 130.4, 128.8, 126.5, 126.2, 126.0, 124.6, 124.1, 124.0, 123.1, 122.4, 117.8, 117.5, 117.0, 116.6, 116.0, 64.1, 63.7, 57.5, 56.9, 22.0, 19.2, 14.2, 12.9. HRMS: m/z calcd for C₃₀H₂₈N₂O₆S + H⁺: 545.1746; found: 545.1749.
Compound 21b: ^¹H NMR (400 MHz, CD₃COCD₃): δ = 10.6 (br s, 1 H), 9.89 (br s, 1 H), 8.12 (s, 1 H), 7.99 (d, J = 8.4 Hz, 1 H), 7.64-7.63 (m, 1 H), 7.23-7.10 (m, 3 H), 7.05-6.95 (m, 2 H), 4.65, 4.60 (ABq, J = 15.2 Hz, 2 H), 4.37, 4.24 (ABq, J = 15.6 Hz, 2 H), 2.61 (s, 3 H), 2.42 (s, 3 H). ^¹³C NMR (100 MHz, CD₃COCD₃): δ = 139.7, 139.3, 136.2, 128.8, 126.7, 126.2, 124.6, 123.6, 123.9, 122.6, 122.5, 121.1, 120.7, 120.0, 119.4, 117.7, 116.9, 116.0, 110.4, 57.1, 56.6, 16.3, 16.1. HRMS: m/z calcd for C₂₄H₂₀N₂O₂S + H⁺: 401.1324; found: 401.1317.
Compound 11c: ^¹H NMR (400 MHz, CDCl₃): δ = 7.99 (d, J = 8.8 Hz, 2 H), 7.78 (s, 2 H), 7.09 (d, J = 2.0 Hz, 2 H), 6.95 (dd, J = 2.0 Hz, 2 H), 4.50-4.43 (m, 8 H), 3.79 (s, 6 H), 1.45 (t, J = 7.2 Hz, 6 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 150.3, 131.3, 130.3, 129.2, 116.3, 114.9, 102.3, 102.2, 80.8, 80.1, 63.9, 55.8, 45.3, 14.5. HRMS: m/z calcd for C₃₀H₂₈N₂O₈S + H⁺: 577.1645; found: 577.1649.
Compound 18c: ^¹H NMR (400 MHz, CDCl₃): δ = 8.16 (d, J = 8.4 Hz, 1 H), 8.00 (d, J = 9.2 Hz, 1 H), 7.96 (s, 1 H), 7.60 (s, 1 H), 7.46 (dd, J = 2.4 Hz, 1 H), 7.11 (dd, J = 2.4 Hz, 1 H), 7.02 (dd, J = 2.4 Hz, 1 H), 6.69 (dd, J = 2.4 Hz, 1 H), 4.60 (s, 2 H), 4.54-4.49 (m, 2 H), 4.46, 4.33 (ABq, J = 16.4 Hz, 2 H), 3.94 (s, 3 H), 3.76-3.72 (m, 4 H), 3.40-3.36 (m, 1 H), 1.48 (t, J = 7.2 Hz, 3 H), 0.80 (t, J = 7.2 Hz, 3 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 156.8, 156.7, 151.5, 150.9, 138.2, 134.6, 130.9, 130.0, 129.7, 128.4, 126.7, 125.5, 123.5, 120.1, 119.1, 117.1, 116.6, 116.4, 116.2, 114.7, 103.2, 102.4, 63.8, 63.4, 57.7, 57.6, 56.1, 55.9, 14.6, 13.8. HRMS: m/z calcd for C₃₀H₂₈N₂O₈S + H⁺ 577.1645; found: 577.1649.
Compound 21c: ^¹H NMR (400 MHz, CD₃COCD₃): δ = 10.6 (br s, 1 H), 9.9 (br s, 1 H), 8.09 (s, 1 H), 7.35 (d, J = 2.0 Hz, 1 H), 7.61 (d, J = 1.6 Hz, 1 H), 7.44 (t, J = 9.2 Hz, 2 H), 7.03 (dd, J = 2.4 Hz, 1 H), 6.86 (dd, J = 2.4 Hz, 1 H), 6.77 (d, J = 2.0 Hz, 1 H), 4.60 (s, 2 H), 4.43, 4.34 (ABq, J = 15.6 Hz, 2 H), 3.88 (s, 3 H), 3.66 (s, 3 H). ^¹³C NMR (100 MHz, CD₃COCD₃): δ = 154.8, 154.2, 139.8, 135.5, 132.0, 128.7, 126.8, 125.5, 125.4, 123.5, 123.2, 122.6, 116.9, 116.2, 115.7, 112.9, 112.8, 112.2, 110.0, 102.9, 100.8, 57.2, 56.7, 55.4, 55.1. HRMS: m/z calcd for C₂₄H₂₀N₂O₄S + H⁺: 433.1222; found: 433.1227.