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Synlett 2009(6): 1004-1008  
DOI: 10.1055/s-0028-1088195
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Convenient Synthesis of Indolo- and Pyrrolobenzazepines via a Threefold Norbornene-Mediated Domino Reaction

Valentina Aureggi, Marion Davoust, Kersten M. Gericke, Mark Lautens*
Department of Chemistry, Davenport Chemical Laboratories, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6, Canada
Fax: +1(416)9468185; e-Mail: mlautens@chem.utoronto.ca;
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Publikationsverlauf

Received 23 October 2008
Publikationsdatum:
16. März 2009 (online)

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Abstract

A practical synthesis of a novel class of fused hetero­cycles was developed from 1-(2-iodobenzyl)-1H-pyrrole and -indoles with various bromoalkyl aryl alkynes. This palladium(0)-catalyzed norbornene-mediated domino reaction allows the efficient formation of three carbon-carbon bonds in a one-pot procedure with PdCl2 and tri-2-furylphosphine (TFP), in the presence of norbornene and Cs2CO3 in acetonitrile at 90 ˚C. New seven-membered-ring fused heterocycles are obtained in moderate to excellent yields.

Key words

norbornene - domino reaction - indoles - pyrroles - palladium

    References and Notes

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8

For the starting material synthesis and the optimization of the reaction conditions, see ref. 2.

9

General Procedure
A 10 mL sealable reaction vessel was charged with 1-(2-iodobenzyl)-1H-indole or -pyrrole (0.36 mmol, 1.2 equiv), bromoalkyl aryl alkyne (0.30 mmol, 1.0 equiv), norbornene (28 mg, 0.30 mmol, 1.0 equiv), Cs2CO3 (293 mg, 0.90 mmol, 3.0 equiv), PdCl2 (5.3 mg, 0.03 mmol, 10 mol%), tri-2-furylphosphine (13.9 mg, 0.06 mmol, 20 mol%), and MeCN (3 mL). The mixture was stirred at r.t. for 10 min while being purged with argon. The tube was sealed and put into a preheated oil bath at 90 ˚C for 24 h. The reaction mixture was diluted with CH2Cl2, filtered onto a short plug of Celite, and washed with CH2Cl2. The solvent was evaporated in vacuo. The crude was purified by SiO2 flash chromatography (pentane → pentane-EtOAc, 50:1, depending on the polarity of the product) to afford the desired compound.
Indole 3aa: ¹H NMR (300 MHz, CDCl3): δ = 7.68 (m, 2 H), 7.50-7.00 (m, 9 H), 6.62 (s, 1 H), 5.90 (s, 1 H), 5.05 (s, 2 H), 2.86 (t, 2 H, J = 6.5 Hz), 2.47 (m, 2 H), 1.90 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 141.9, 140.6, 135.8, 134.5, 133.0, 129.6, 128.7, 128.6, 128.3, 128.0, 127.9, 127.2, 127.1, 123.7, 121.9, 121.7, 121.1, 119.8, 109.4, 91.5, 48.6, 31.5, 30.4, 24.3 ppm. HRMS (EI): m/z calcd for C26H21N [M+]: 347.1674; found: 347.1671.
Indole 3ab: ¹H NMR (300 MHz, CDCl3): δ = 8.35-8.29 (m, 2 H), 7.56-7.49 (m, 3 H), 7.46-7.42 (m, 1 H), 7.31-7.12 (m, 4 H), 7.06-6.99 (m, 1 H), 5.83 (s, 1 H), 5.18 (s, 2 H), 2.89 (t, 2 H, J = 6.7 Hz), 2.47-2.40 (m, 2 H), 1.93 (mc, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 149.4, 147.3, 140.3, 139.1, 135.9, 135.7, 135.3, 130.8, 130.3, 128.8, 128.6, 128.1, 125.8, 124.2, 122.2, 121.0, 120.0, 108.9, 102.7, 47.9, 31.7, 30.2, 24.2 ppm. HRMS (EI): m/z calcd for C26H20N2O2 [M+]: 392.1520; found: 392.1525.
Indole 3ac: ¹H NMR (300 MHz, CDCl3): δ = 7.50 (m, 2 H), 7.43 (m, 2 H), 7.38 (m, 1 H), 7.33 (m, 1 H), 7.28 (m, 1 H), 7.24 (m, 1 H), 7.19 (m, 1 H), 7.12 (m, 1 H), 7.0 (dt, 1H, J = 7.1, 7.9 Hz), 5.94 (s, 1 H), 5.23 (d, 1 H, J = 13.9 Hz), 5.17 (d, 1 H, J = 13.9 Hz), 2.80 (m, 2 H), 2.48 (m, 1 H), 2.35 (m, 1 H), 1.86 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 140.6, 140.4, 138.8, 135.9, 135.6, 135.4, 135.0, 133.4, 130.6, 129.9, 129.3, 128.6, 128.1 (2), 128.0, 127.0, 125.6, 121.4, 120.7, 119.4, 108.6, 101.2, 47.7, 31.0, 30.3, 23.5 ppm. HRMS (EI): m/z calcd for C26H20NCl [M+]: 381.1284; found: 381.1293.
Indole 3ad: ¹H NMR (300 MHz, CDCl3): δ = 7.50 (br d, 1 H, J = 6.1 Hz), 7.44-7.32 (m, 2 H), 7.30-6.94 (m, 8 H), 5.95 (s, 1 H), 5.17 (s, 2 H), 3.73 (s, 3 H), 2.85-2.78 (m, 2 H), 2.57-2.45 (m, 1 H), 2.41-2.30 (m, 1 H), 1.86 (mc, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 156.8, 140.4, 140.3, 136.3, 136.1, 135.6, 134.9, 131.5, 130.7, 128.8, 128.6, 128.4, 128.3, 127.9, 125.6, 121.3, 120.9, 120.8, 119.4, 111.5, 108.7, 101.0, 55.9, 47.9, 31.4, 30.6, 23.9. HRMS (EI): m/z calcd for C27H23NO [M+]: 377.1780; found: 377.1780.
Indole 3bd: ¹H NMR (300 MHz, CDCl3): δ = 8.18 (br s, 1 H), 7.87 (d, 1 H, J = 8.6 Hz), 7.45 (d, 1 H, J = 8.8 Hz), 7.37 (br t, 1 H, J = 7.8 Hz), 7.32-7.18 (m, 4 H), 7.15-6.96 (m, 3 H), 6.04 (s, 1 H), 5.18 (s, 2 H), 3.88 (s, 3 H), 3.74 (s, 3 H), 2.86-2.78 (m, 2 H), 2.60-2.45 (m, 1 H), 2.42-2.28 (m, 1 H), 1.94-1.80 (mc, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 168.5, 156.7, 141.7, 140.5, 137.8, 136.1, 135.9, 135.6, 131.1, 130.6, 129.0, 128.6, 128.2, 127.8, 125.7, 123.8, 122.7, 121.4, 121.0, 111.5, 108.3, 102.3, 55.9, 51.9, 48.1, 31.4, 30.6, 23.8. HRMS (EI): m/z calcd for C29H26NO3 [M + H+]: 436.1926; found: 436.1907.
Indole 3ae: ¹H NMR (300 MHz, CDCl3): δ = 8.06 (m, 2 H), 7.52 (m, 3 H), 7.42 (d, 1 H, J = 7.9 Hz), 7.28-7.15 (m, 4 H), 7.00 (m, 1 H), 5.85 (s, 1 H), 5.17 (s, 2 H), 4.38 (q, 2 H, J = 7.1 Hz), 2.86 (t, 2 H, J = 6.5 Hz), 2.45 (t, 2 H, J = 6.3 Hz), 1.90 (m, 2 H), 1.39 (t, 3 H, J = 7.1 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 166.8, 142.8, 140.2 (2), 136.3, 135.8, 135.7, 134.9, 134.1, 131.5, 131.2, 130.8, 128.8, 128.4, 128.5, 128.3, 128.2, 125.7, 121.9, 120.9, 119.8, 108.8,102.6, 61.3, 47.9, 31.7, 30.3, 24.3, 14.6. HRMS (EI): m/z calcd for C29H25NO2 [M+]: 419.1885; found: 419.1882.
Indole 3af: ¹H NMR (300 MHz, CDCl3): δ = 7.95 (d, 1 H, J = 8.3 Hz), 7.90 (m, 2 H), 7.60-7.30 (m, 8 H), 7.16 (m, 2 H), 6.96 (m, 1 H), 5.84 (s, 1 H), 5.30 (s, 2 H), 2.82 (t, 2 H, J = 6.4 Hz), 2.47 (m, 1 H), 2.24 (m, 1 H), 1.78 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 140.6, 140.0, 135.9, 135.7 (2), 134.2, 131.8, 130.4, 128.6 (2), 128.5, 128.3 (2), 128.2, 127.7, 126.8, 126.5, 126.1, 126.0(2), 125.8, 121.7, 120.9, 119.6, 108.7, 102.0, 48.2, 31.5, 30.6, 24.0. HRMS (EI):
m/z calcd for C30H23N [M+]: 397.1813; found: 397.1843.
Indole 3ag: ¹H NMR (300 MHz, CDCl3): δ = 8.10-8.05 (m, 1 H), 7.82-7.77 (m, 2 H), 7.60 (s, 1 H), 7.51 (br d, 1 H, J = 8.2 Hz), 7.38-7.11 (m, 10 H), 6.99 (mc, 1 H), 5.79 (s,
1 H), 5.20 (s, 2 H), 2.84 (t, 2 H, J = 6.5 Hz), 2.52-2.42
(m, 2 H), 2.37 (s, 3 H), 1.96 (mc, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 145.2, 140.4, 137.8, 136.1, 135.9, 135.7, 135.5, 135.4, 131.2, 130.1, 128.6, 128.4, 128.2, 127.0, 125.7, 125.2, 124.6, 123.9, 121.9, 121.8, 120.8, 120.6, 119.7, 114.3, 108.8, 101.6, 139.5, 124.4, 48.0, 31.6, 30.4, 24.3, 21.9. HRMS (EI): m/z calcd for C35H29N2O2S [M + H+]: 541.1921; found: 541.1944.
Indole 3bg: ¹H NMR (300 MHz, CDCl3): δ = 8.12-8.07 (m, 2 H), 7.89 (dd, 1 H, J = 8.7, 1.6 Hz), 7.81-7.76 (m, 2 H), 7.60 (s, 1 H), 7.50 (br d, 1 H, J = 8.9 Hz), 7.39-7.14 (m, 8 H), 5.80 (s, 1 H), 5.21 (s, 2 H), 3.88 (s, 3 H), 2.86 (t, 2 H, J = 6.5 Hz), 2.55-2.45 (m, 2 H), 2.41 (s, 3 H), 1.96 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 168.3, 145.4, 140.6, 138.8, 137.9, 135.9, 135.6, 135.4, 135.4, 131.0, 130.2, 128.9, 128.7, 127.6, 127.0, 125.8, 125.3, 124.7, 124.2, 124.0, 123.8, 123.1, 121.7, 121.5, 120.4, 114.4, 108.5, 102.9, 52.0, 48.3, 31.7, 30.4, 24.2, 21.8. HRMS (EI): m/z calcd for C37H31ON2O4S [M + H+]: 599.1968; found: 599.1999.
Pyrrole 5a: ¹H NMR (300 MHz, CDCl3): δ = 7.40 (m, 1 H), 7.30 (m, 4 H), 7.18 (d, 1 H, J = 7.3 Hz), 7.12 (m, 2 H), 6.70 (m, 1 H, J = 2.5 Hz), 6.04 (dd, 1 H, J = 3.7, 2.6 Hz), 5.58 (dd, 1 H, J = 3.7, 1.8 Hz), 4.93 (s, 2 H), 2.84 (t, 2 H, J = 6.5 Hz), 2.40 (br s, 2 H), 1.90-1.82 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 142.9, 139.9, 136.7, 135.4, 132.7, 130.3, 129.5, 128.5 (2), 128.2, 127.6, 126.9, 125.5, 120.5, 110.1, 108.4, 52.8, 31.2, 30.6, 24.5. HRMS (EI): m/z calcd for C22H19N [M+]: 297.1517; found: 297.1522.
Pyrrole 5b: ¹H NMR (400 MHz, CDCl3): δ = 8.29 (d, 2 H, J = 8.8 Hz), 7.48 (d, 2 H, J = 8.8 Hz), 7.24-7.22 (m, 1 H), 7.16-7.13 (m, 2 H), 6.74 (dd, 1 H, J = 2.5, 1.8 Hz), 6.07 (dd, 1 H, J = 3.7, 2.6 Hz), 5.52 (dd, 1 H, J = 3.7, 1.7 Hz), 4.96 (s, 2 H), 2.87 (t, 2 H, J = 6.5 Hz), 2.37 (t, 2 H, J = 6.5 Hz), 1.88 (quint, 2 H, J = 6.5 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 149.7, 147.0, 139.9, 135.9, 135.3, 132.8, 131.1, 130.6, 130.4, 128.6, 128.1, 125.6, 123.9, 121.1, 110.2, 108.6, 52.7, 31.2, 30.3, 24.3. HRMS (EI): m/z calcd for C22H18N2O2 [M+]: 342.1368; found: 342.1383.
Pyrrole 5c: ¹H NMR (300 MHz, CDCl3): δ = 7.46 (m, 1 H), 7.30 (m, 4 H), 7.14-7.02 (m, 2 H), 6.69 (dd, 1 H, J = 2.5, 1.8 Hz), 6.05 (dd, 1 H, J = 3.6, 2.6 Hz), 5.62 (dd, 1 H, J = 3.6, 1.6 Hz), 4.89 (s, 2 H), 2.83-2.70 (m, 2 H), 2.39 (m, 1 H), 2.28 (m, 1 H), 1.81 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 141.0, 140.5, 135.7, 135.5, 132.4, 130.9, 130.5, 129.7, 129.5, 128.3, 127.9 (2), 127.6, 126.9, 125.5, 120.3, 108.9, 108.3, 52.4, 30.6, 30.5, 23.6. HRMS (EI): m/z calcd for C22H18NCl [M+]: 331.1128; found: 331.1136.
Pyrrole 5d: ¹H NMR (300 MHz, CDCl3): δ = 7.34-7.29 (m, 1 H), 7.20-7.08 (m, 4 H), 7.02-6.95 (m, 2 H), 6.66 (dd, 1 H, J = 2.4, 1.8 Hz), 6.03 (dd, 1 H, J = 3.6, 2.6 Hz), 5.64 (dd, 1 H, J = 3.6, 1.7 Hz), 4.97 (d, 1 H, J = 13.5 Hz), 4.90 (d, 1 H, J = 13.4 Hz) 3.75 (s, 3 H), 2.80-2.76 (m, 2 H), 2.42-2.28 (m, 2 H), 1.85-1.79 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 157.4, 138.9, 134.5, 130.6, 129.6, 129.5, 127.2, 126.9, 126.2, 124.3, 123.8, 119.6, 118.8, 117.6, 110.1 (2), 107.6, 107.0, 54.6, 51.4, 29.8, 29.6, 22.7. HRMS (EI): m/z calcd for C23H21NO [M+]: 327.1627; found: 327.1623.
Pyrrole 5e: ¹H NMR (300 MHz, CDCl3): δ = 8.04-8.00 (m, 1 H), 7.99-7.97 (m, 1 H), 7.50-7.48 (m, 2 H), 7.22-7.19 (m, 1 H), 7.15-7.10 (m, 2 H), 6.72 (dd, 1 H, J = 1.8, 2.5 Hz), 6.04 (dd, 1 H, J = 2.5, 3.7 Hz), 5.54 (dd, 1 H, J = 1.8, 3.7 Hz), 4.94 (s, 2 H), 4.38 (q, 2 H, J = 7.1 Hz), 2.84 (t, 2 H, J = 6.4 Hz), 2.37 (m, 2 H), 1.86 (quint, 2 H, J = 6.4 Hz), 1.39 (t, 3 H, J = 7.1 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 166.8, 143.0, 139.9, 136.3, 135.4, 133.9, 133.8, 131.6, 130.9, 130.7 (2), 128.6, 128.4, 128.1, 127.7, 125.5, 120.7, 110.1, 108.4, 61.2, 52.7, 31.2, 30.4, 24.3, 14.5. HRMS (EI): m/z calcd for C25H23NO2 [M+]: 369.1729; found: 369.1721.
Pyrrole 5f: ¹H NMR (300 MHz, CDCl3): δ = 7.92 (d, 1 H, 8.3 Hz), 7.86 (m, 2 H), 7.53 (m, 1 H), 7.46 (m, 1 H), 7.40 (m, 2 H), 7.23 (d, 1 H, J = 9.2 Hz), 7.20 (m, 1 H), 7.14 (m, 1 H), 6.71 (dd, 1 H, J = 2.5, 1.8 Hz), 5.97 (dd, 1 H, J = 3.7, 2.6 Hz), 5.51 (br s, 1 H), 5.06 (s, 2 H), 2.78 (t, 2 H, J = 6.2 Hz), 2.38 (m, 1 H), 2.17 (m, 1 H), 1.73 (m, 2 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 140.3 (2), 136.4, 135.5, 134.1, 133.8, 131.7, 128.5 (2), 128.3, 127.7, 127.3, 126.3, 126.1, 126.0(2), 125.7, 120.7, 120.6, 109.7, 108.5, 53.0, 31.0, 30.8, 24.0. HRMS (EI): m/z calcd for C26H21N [M+]: 347.1674; found: 347.1667.
Pyrrole 5g: ¹H NMR (400 MHz, CDCl3): δ = 7.23-7.16 (m, 5 H), 7.14-7.10 (m, 2 H), 6.70-6.69 (m, 1 H), 6.05 (dd, 1 H, J = 3.7, 2.6 Hz), 5.60 (dd, 1 H, J = 3.7, 1.7 Hz), 4.93 (s, 2 H), 2.85 (t, 2 H, J = 6.5 Hz), 2.43-2.39 (m, 2 H), 2.41 (s, 3 H), 1.87 (quint, 2 H, J = 6.4 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 139.9, 139.8, 136.7, 136.3, 135.3, 132.6, 130.2, 129.3, 129.1, 128.9, 128.3, 127.4, 125.3, 120.4, 109.9, 108.3, 52.7, 31.1, 30.5, 24.5, 21.4. HRMS (EI): m/z calcd for C23H21N [M+]: 311.1674; found: 311.1668.
Pyrrole 5h: ¹H NMR (300 MHz, CDCl3): δ = 7.23-7.18 (m, 1 H), 7.13-7.08 (m, 2 H), 6.72 (dd, 1 H, J = 2.3, 2.0 Hz), 6.51 (s, 2 H), 6.08 (dd, 1 H, J = 3.7, 2.6 Hz), 5.73 (dd, 1 H, J = 3.7, 1.7 Hz), 4.93 (s, 2 H), 3.91 (s, 3 H), 3.86 (s, 6 H), 2.86 (t, 2 H, J = 6.5 Hz), 2.48-2.40 (m, 2 H), 1.89 (quint, 2 H, J = 6.4 Hz). ¹³C NMR (100 MHz, CDCl3): δ = 153.3, 139.7, 138.3, 136.8, 136.5, 135.3, 133.8, 132.4, 130.4, 128.4, 127.6, 125.4, 120.6, 109.8, 108.3, 106.4, 61.1, 56.3, 52.7, 31.1, 30.4, 24.5. ESI-HRMS: m/z calcd for C25H26NO3 [M + H+]: 388.1894; found: 388.1907.
Compound 7b: ¹H NMR (400 MHz, CDCl3): δ = 8.12-8.09 (m, 2 H), 7.77-7.74 (m, 1 H), 7.23-7.19 (m, 1 H), 7.13-7.08 (m, 2 H), 6.49 (t, 2 H, J = 2.1 Hz), 6.08 (t, 2 H, J = 2.1 Hz), 5.32 (d, 1 H, J = 14.6 Hz), 5.01 (d, 1 H, J = 14.6 Hz), 3.31-3.23 (m, 1 H), 3.09 (d, 1 H, J = 7.7 Hz), 2.92 (d, 1 H, J = 7.8 Hz), 2.64 (dt, 1 H, J = 13.8, 3.1 Hz), 2.57-2.51 (m, 1 H), 2.35 (d, 1 H, J = 4.2 Hz), 2.30 (dt, 1 H, J = 4.3, 13.5 Hz), 2.14-2.07 (m, 1 H), 1.56-1.47 (m, 1 H), 1.46-1.36 (m, 2 H), 1.35-1.19 (m, 2 H), 0.96-0.81 (m, 3 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 151.7, 149.6, 147.1, 142.8, 142.2, 138.2, 135.4, 134.0, 127.9, 127.5, 126.0, 125.1, 122.3, 121.0, 120.5, 108.3, 53.6, 52.0, 51.4, 43.7, 41.1, 32.6, 30.1, 29.6, 29.1, 28.4, 22.8. HRMS (EI): m/z calcd for C29H28N2O2 [M+]: 436.2151; found: 436.2166.
Compound 7e: ¹H NMR (400 MHz, CDCl3): δ = 8.34 (br s, 1 H), 7.92 (dd, 1 H, J = 7.9, 1.2 Hz), 7.32 (d, 1 H, J = 7.9 Hz), 7.18-7.14 (m, 1 H), 7.10-7.03 (m, 2 H), 6.54 (t, 2 H, J = 2.1 Hz), 6.09 (t, 2 H, J = 2.1 Hz), 5.33 (d, 1 H, J = 14.6 Hz), 5.02 (d, 1 H, J = 14.6 Hz), 4.45-4.37 (m, 2 H), 3.41-3.33 (m, 1 H), 3.04 (d, 1 H, J = 7.6 Hz), 2.85 (d, 1 H, J = 7.5 Hz), 2.66-2.55 (m, 2 H), 2.34-2.26 (m, 2 H), 2.15-2.07 (m, 1 H), 1.56-1.45 (m, 1 H), 1.44-1.34 (m, 2 H), 1.42 (t, 3 H, J = 7.1 Hz), 1.33-1.17 (m, 2 H), 0.96-0.94 (m, 1 H), 0.91-0.84 (m, 1 H), 0.79-0.76 (m, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 171.3, 167.1, 155.6, 143.5, 142.8, 138.7, 134.0, 131.0, 129.2, 129.0, 127.3, 127.0, 126.3, 125.7, 125.2, 121.0, 108.2, 61.1, 53.4, 52.5, 51.2, 43.7, 41.0, 32.7, 30.2, 29.3, 29.2, 28.5, 23.2, 14.6. HRMS (EI): m/z calcd for C32H33NO2 [M+]: 463.2511; found: 463.2519.