Transition Metals in Organic Synthesis, Part 87: [¹] An Efficient Palladium-­Catalyzed Route to 2-Oxygenated and 2,7-Dioxygenated Carbazole Alkaloids - Total Synthesis of 2-Methoxy-3-methylcarbazole, Glycosinine, Clausine L, Mukonidine, and Clausine V

Abstract

Optimization of the palladium(II)-catalyzed oxidative cyclization of N,N-diarylamines opens up the way to an efficient synthesis of 2-oxygenated and 2,7-dioxygenated carbazole alkaloids including 2-methoxy-3-methylcarbazole, glycosinine, clausine L, mukonidine, and clausine V.

alkaloids - antibiotics - catalysis - cyclizations - palladium

References and Notes

1 Part 86: Forke R. Jäger A. Knölker H.-J. Org. Biomol. Chem.  2008,  6 , in press

For some comprehensive reviews, see:

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2b Chakraborty DP. In The Alkaloids   Vol. 44:  Cordell GA. Academic Press; New York: 1993.  p.257 

2c Knölker H.-J. Reddy KR. Chem. Rev.  2002,  102:  4303 

2d Knölker H.-J. Top. Curr. Chem.  2005,  244:  115 

2e Knölker H.-J. Reddy KR. In The Alkaloids   Vol. 65:  Cordell GA. Academic Press; Amsterdam: 2008.  p.1 

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3a Pindur U. Chimia  1990,  44:  406 

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3g Lemster T. Pindur U. Recent Res. Dev. Org. Bioorg. Chem.  2002,  5:  99 

3h Knölker H.-J. Curr. Org. Synth.  2004,  1:  309 

3i Fröhner W. Krahl MP. Reddy KR. Knölker H.-J. Heterocycles  2004,  63:  2393 

Recent contributions:

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4c Yamamoto M. Matsubara S. Chem. Lett.  2007,  36:  172 

4d Forke R. Krahl MP. Krause T. Schlechtingen G. Knölker H.-J. Synlett  2007,  268 

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11 Bhattacharyya P. Chowdhury BK. Indian J. Chem., Sect. B: Org. Chem. Incl. Med. Chem.  1985,  24:  452 

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18a Knölker H.-J. Wolpert M. Tetrahedron Lett.  1997,  38:  533 

18b Knölker H.-J. Wolpert M. Tetrahedron  2003,  59:  5317 

19 Kataeva O. Krahl MP. Knölker H.-J. Org. Biomol. Chem.  2005,  3:  3099 

20 Krahl MP. Jäger A. Krause T. Knölker H.-J. Org. Biomol. Chem.  2006,  4:  3215 

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22g Knölker H.-J. Knöll J. Chem. Commun.  2003,  1170 

23

Characteristic Spectroscopic Data of the 2-Oxygenated and 2,7-Dioxygenated Carbazole Alkaloids2-Methoxy-3-methylcarbazole (4)
Colorless crystals; mp 221 ˚C (lit.^¹¹ 223 ˚C). UV (MeOH): λ_max = 230, 237, 257, 264 (sh), 301, 331 nm. IR (ATR): ν = 3402, 2992, 2919, 2851, 1631, 1609, 1496, 1455, 1340, 1304, 1230, 1194, 1175, 1139, 1109, 1038, 1014, 1003, 885, 819, 766, 749, 725 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 2.32 (s, 3 H), 3.89 (s, 3 H), 7.02 (s, 1 H), 7.12 (t, J = 7.8 Hz, 1 H), 7.27 (t, J = 7.8 Hz, 1 H), 7.43 (d, J = 7.8 Hz, 1 H), 7.82 (s, 1 H), 7.97 (d, J = 7.8 Hz, 1 H), 10.05 (br s, 1 H). ^¹³C NMR and DEPT (125 MHz, acetone-d ₆): δ = 16.87 (CH₃), 55.68 (CH₃), 93.35 (CH), 111.27 (CH), 116.73 (C), 118.95 (C), 119.43 (CH), 119.79 (CH), 121.94 (CH), 124.14 (C), 124.60 (CH), 140.61 (C), 140.74 (C), 158.20 (C). MS (EI): m/z (%) = 211 (100) [M⁺], 210 (11), 196 (77), 180 (7), 168 (25), 167 (35), 166 (10). Anal. Calcd (%) for C₁₄H₁₃NO: C, 79.59; H, 6.20; N, 6.63. Found: C, 79.12; H, 6.64; N, 6.13.
Glycosinine ( O -Methylmukonal) (5)
Colorless crystals; mp 196-198 ˚C (lit.^¹² 189.0-189.5 ˚C, lit.^¹³ 185 ˚C). UV (MeOH): λ_max = 235, 243 (sh), 276, 295, 351 nm. IR (ATR): ν = 3323, 2922, 2851, 1664, 1603, 1575, 1487, 1460, 1436, 1412, 1381, 1345, 1328, 1309, 1259, 1244, 1200, 1169, 1145, 1030, 974, 917, 901, 854, 841, 764, 744, 724 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 4.02 (s, 3 H), 7.16 (s, 1 H), 7.22 (t, J = 7.8 Hz, 1 H), 7.37 (t, J = 7.8 Hz, 1 H), 7.49 (d, J = 7.8 Hz, 1 H), 8.14 (d, J = 7.8 Hz, 1 H), 8.51 (s, 1 H), 10.46 (s, 1 H), 10.66 (br s, 1 H). ^¹³C NMR and DEPT (75 MHz, acetone-d ₆): δ = 56.32 (CH₃), 93.78 (CH), 111.89 (CH), 117.95 (C), 119.58 (C), 120.74 (CH), 120.95 (CH), 121.35 (CH), 124.38 (C), 126.37 (CH), 141.61 (C), 146.43 (C), 162.37 (C), 188.57 (CHO). MS (EI): m/z (%) = 225 (100) [M⁺], 224 (26), 210 (9), 209 (14), 208 (22), 196 (8), 180 (21), 179 (42), 168 (21), 154 (28). Anal. Calcd (%) for C₁₄H₁₁NO₂: C, 74.65; H, 4.92; N, 6.22. Found: C, 74.77; H, 4.98; N, 6.19.
Clausine L (6)
Colorless crystals; mp 172-173 ˚C (lit.⁸ 133-135 ˚C; lit.⁹ 204-205 ˚C). UV (MeOH): λ_max = 235, 241, 269, 282 (sh), 319, 333 nm. IR (ATR): ν = 3264, 2951, 2922, 2852, 1690, 1632, 1608, 1574, 1486, 1462, 1427, 1392, 1348, 1313, 1278, 1239, 1201, 1163, 1115, 1082, 1035, 979, 950, 909, 875, 825, 789, 775, 766, 750, 727 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 3.85 (s, 3 H), 3.92 (s, 3 H), 7.15 (s, 1 H), 7.20 (t, J = 7.8 Hz, 1 H), 7.35 (t, J = 7.8 Hz, 1 H), 7.49 (d, J = 7.8 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H), 8.54 (s, 1 H), 10.53 (br s, 1 H). ^¹³C NMR and DEPT (75 MHz, acetone-d ₆): δ = 51.77 (CH₃), 56.44 (CH₃), 94.85 (CH), 111.83 (CH), 113.76 (C), 116.97 (C), 120.47 (CH), 120.63 (CH), 124.19 (C), 124.99 (CH), 126.00 (CH), 141.53 (C), 144.70 (C), 159.83 (C), 167.45 (C=O). MS (EI): m/z (%) = 255 (100) [M⁺], 240 (5), 224 (89), 209 (18), 194 (9), 181 (7), 166 (14), 153 (15), 139 (11). HRMS: m/z calcd for C₁₅H₁₃NO₃ [M⁺]: 255.0895; found: 255.0889.
Mukonidine (3) Colorless crystals; mp 189 ˚C (lit.⁸ 168-170 ˚C; lit.^¹0 188 ˚C). UV (MeOH): λ_max = 235, 243, 270 (sh), 276 (sh), 284, 325, 338 nm. IR (ATR): ν = 3347, 2952, 2922, 2852, 1644, 1627, 1582, 1481, 1464, 1432, 1373, 1363, 1329, 1258, 1236, 1189, 1165, 1118, 1093, 1014, 991, 949, 898, 871, 821, 784, 762, 740, 719 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 4.00 (s, 3 H), 6.93 (s, 1 H), 7.20 (t, J = 7.8 Hz, 1 H), 7.36 (t, J = 7.8 Hz, 1 H), 7.47 (d, J = 7.8 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H), 8.62 (s, 1 H), 10.52 (br s, 1 H), 11.07 (s, 1 H). ^¹³C NMR and DEPT (75 MHz, acetone-d ₆): δ = 52.60 (CH₃), 97.70 (CH), 105.95 (C), 111.79 (CH), 117.85 (C), 120.58 (CH), 120.89 (CH), 123.41 (CH), 124.30 (C), 126.51 (CH), 141.96 (C), 146.62 (C), 161.62 (C), 172.22 (C=O). MS (EI): m/z (%) = 241 (46) [M⁺], 209 (100), 181 (20), 153 (33), 126 (10), 104 (10).
Isomukonidine (13)
Colorless crystals; mp 226 ˚C (decomp.) (‘Chakraborty’s mukonidine’, lit.⁷ 245 ˚C). UV (EtOH): λ_max = 235, 241, 269, 278 (sh), 281, 320, 334 nm. IR (ATR): ν = 3206, 3180, 2922, 2851, 1702, 1625, 1608, 1582, 1492, 1459, 1439, 1357, 1328, 1303, 1246, 1224, 1192, 1159, 1078, 1024, 1010, 968, 914, 874, 819, 778, 764, 751, 716 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 4.13 (s, 3 H), 7.24 (t, J = 7.8 Hz, 1 H), 7.27 (s, 1 H), 7.39 (t, J = 7.8 Hz, 1 H), 7.51 (d, J = 7.8 Hz, 1 H), 8.16 (d, J = 7.8 Hz, 1 H), 8.77 (s, 1 H), 10.62 (br s, 1 H), 10.88 (br s, 1 H). ^¹³C NMR and DEPT (125 MHz, acetone-d ₆): δ = 57.08 (CH₃), 94.56 (CH), 111.62 (C), 111.88 (CH), 118.10 (C), 120.72 (CH), 120.84 (CH), 123.97 (C), 126.24 (CH), 126.37 (CH), 141.58 (C), 145.02 (C), 158.90 (C), 166.56 (C=O). MS (EI): m/z (%) = 241 (100) [M⁺], 226 (5), 224 (9), 194 (5), 182 (11), 168 (6), 154 (14), 153 (6). Anal. Calcd (%) for C₁₄H₁₁NO₃: C, 69.70; H, 4.60; N, 5.81. Found: C, 69.84; H, 4.81; N, 5.92.
3-Cyano-7-hydroxy-2-methoxycarbazole (19)
Colorless crystals; mp 251-252 ˚C. UV (MeOH): λ_max = 220, 244, 282, 322, 336 nm. IR (ATR): ν = 3529, 3385, 3364, 3324, 3205, 2923, 2841, 2219, 1612, 1574, 1474, 1450, 1429, 1400, 1357, 1322, 1283, 1263, 1243, 1202, 1143, 1115, 1026, 954, 899, 845, 819, 810, 721 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 3.97 (s, 3 H), 6.79 (dd, J = 8.4, 2.1 Hz, 1 H), 6.94 (d, J = 2.1 Hz, 1 H), 7.14 (s, 1 H), 7.89 (d, J = 8.4 Hz, 1 H), 8.21 (s, 1 H), 8.47 (br s, 1 H), 10.45 (br s, 1 H). ^¹³C NMR and DEPT (125 MHz, acetone-d ₆): δ = 56.43 (CH₃), 93.45 (C), 94.23 (CH), 97.72 (CH), 110.21 (CH), 116.10 (C), 118.26 (C), 118.47 (C), 121.41 (CH), 125.36 (CH), 142.88 (C), 144.55 (C), 157.40 (C), 159.90 (C). Anal. Calcd (%) for C₁₄H₁₀N₂O₂: C, 70.58; H, 4.23; N, 11.76. Found: C, 70.99; H, 4.71; N, 11.30.
3-Cyano-2,7-dihydroxycarbazole (20)
Colorless crystals; mp >260 ˚C (decomp.). UV (MeOH): λ_max = 220, 244, 277, 282, 323, 337 nm. IR (ATR): ν = 3349, 3315, 2921, 2851, 2218, 1613, 1475, 1448, 1420, 1393, 1326, 1283, 1216, 1190, 1145, 987, 953, 882, 844, 822, 806, 789, 752, 724 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 6.77 (dd, J = 8.4, 2.1 Hz, 1 H), 6.91 (d, J = 2.1 Hz, 1 H), 7.05 (s, 1 H), 7.88 (d, J = 8.4 Hz, 1 H), 8.16 (s, 1 H), 8.46 (br s, 1 H), 9.44 (br s, 1 H), 10.29 (br s, 1 H). ^¹³C NMR and DEPT (125 MHz, acetone-d ₆): δ = 92.51 (C), 97.62 (CH), 97.82 (CH), 110.06 (CH), 116.31 (C), 118.45 (C), 118.80 (C), 121.34 (CH), 124.87 (CH), 143.15 (C), 144.93 (C), 157.49 (C), 157.92 (C).
7-Hydroxy- O -methylmukonal (22) Light yellow crystals; mp >240 ˚C (decomp.). UV (MeOH): λ_max = 223, 242, 284 (sh), 300, 348 nm. IR (ATR): ν = 3384, 3310, 2920, 2846, 1655, 1603, 1583, 1498, 1469, 1400, 1364, 1320, 1236, 1199, 1157, 1104, 1036, 953, 921, 907, 860, 842, 817, 800, 745, 735 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 3.99 (s, 3 H), 6.79 (dd, J = 8.4, 2.1 Hz, 1 H), 6.94 (d, J = 2.1 Hz, 1 H), 7.08 (s, 1 H), 7.92 (d, J = 8.4 Hz, 1 H), 8.35 (s, 1 H), 8.45 (br s, 1 H), 10.41 (br s, 1 H), 10.44 (s, 1 H). ^¹³C NMR and DEPT (125 MHz, acetone-d ₆): δ = 56.26 (CH₃), 93.69 (CH), 98.04 (CH), 110.15 (CH), 117.14 (C), 118.49 (C), 119.25 (C), 119.79 (CH), 121.49 (CH), 143.23 (C), 146.54 (C), 157.47 (C), 161.59 (C), 188.56 (CHO). Anal. Calcd (%) for C₁₄H₁₁NO₃: C, 69.70; H, 4.60; N, 5.81. Found: C, 69.89; H, 4.84; N, 5.44.
Clausine V (9)
Colorless crystals; mp >270 ˚C (decomp.) (lit.^¹5 228-230 ˚C; lit.^³³ 272-274 ˚C). UV (MeOH): λ_max = 224 (sh), 227, 231, 236 (sh), 238, 259, 311, 319 nm. IR (ATR): ν = 3378, 2937, 2837, 1607, 1573, 1502, 1453, 1323, 1263, 1230, 1198, 1156, 1118, 1025, 934, 823, 803, 728 cm^-¹. ^¹H NMR (500 MHz, acetone-d ₆): δ = 3.84 (s, 6 H), 6.76 (dd, J = 8.5, 2.2 Hz, 2 H), 6.98 (d, J = 2.2 Hz, 2 H), 7.84 (d, J = 8.5 Hz, 2 H), 10.07 (br s, 1 H). ^¹³C NMR and DEPT (125 MHz, acetone-d ₆): δ = 55.66 (2 CH₃), 95.55 (2 CH), 108.37 (2 CH), 117.97 (2 C), 120.59 (2 CH), 142.27 (2 C), 159.11 (2 C). MS (EI): m/z (%) = 227 (100) [M⁺], 212 (92), 184 (19), 169 (17), 141 (6). Anal. Calcd (%) for C₁₄H₁₃NO₂: C, 73.99; H, 5.77; N, 6.16. Found: C, 73.55; H, 6.16; N, 6.68.

24 Lafrance M. Fagnou K. J. Am. Chem. Soc.  2006,  128:  16496 

25

Crystal Data for Glycosinine (5)
C₁₄H₁₁NO₂, crystal size: 0.34 × 0.21 × 0.09 mm^³, M = 225.24 g mol^-¹, monoclinic, space group: P2₁/c, λ = 0.71073 Å, a = 11.235 (1), b = 13.717 (1), c = 7.259 (2) Å, β = 106.38 (1)˚, V = 1073.3 (3) Å^³, Z = 4, D _calcd = 1.394
g cm^-³, µ = 0.094 mm^-¹, T = 198 (2) K, θ range = 3.28-30.00˚; reflections collected: 26896, independent: 3108 (R _int = 0.0999), 159 parameters. The structure was solved by direct methods and refined by full-matrix least-squares on F ^²; final R indices [I > 2σ(I)]: R1 = 0.0514, wR2 = 0.1018; maximal residual electron density: 0.273 e Å^-³. CCDC-686500 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.uk/data_request/cif.

26a

Manganese dioxide (precipitated, active) from Merck (art. 805958).

26b Corey EJ. Gilman NW. Ganem BE. J. Am. Chem. Soc.  1968,  90:  5616 

26c Knölker H.-J. J. Prakt. Chem.  1995,  337:  75 

27

Crystal Data for Isomukonidine (13)
C₁₄H₁₁NO₃, crystal size: 0.32 × 0.29 × 0.28 mm^³, M = 241.24 g mol^-¹, monoclinic, space group: C2/c, λ = 0.71073 Å, a = 16.423 (3), b = 7.5231 (15), c = 18.548 (4) Å, β = 96.25 (3)˚, V = 2278.1 (8) Å^³, Z = 8, D _calcd = 1.407 g cm^-³, µ = 0.100 mm^-¹, T = 298 (2) K, θ range = 3.13-30.02˚; reflections collected: 34016, independent: 3328 (R _int = 0.0590), 168 parameters. The structure was solved by direct methods and refined by full-matrix least-squares on F ^²; final R indices [I > 2σ(I)]: R1 = 0.0430, wR2 = 0.1125; maximal residual electron density: 0.316 e Å^-³. CCDC-686501 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.uk/data_request/cif.

28 Sridharan V. Martín MA. Menéndez JC. Synlett  2006,  2375 

29

Experimental Procedure for the Microwave-Assisted Palladium(II)-Catalyzed Oxidative Cyclization The diarylamine 16 (400 mg, 1.01 mmol), Pd(OAc)₂ (46.3 mg, 0.21 mmol), Cu(OAc)₂ (458 mg, 2.52 mmol), and pivalic acid (4.7 g) were heated in a 10 mL microwave vessel for 2 h at 130 ˚C. The reaction mixture was extracted with a sat. solution of K₂CO₃ until the aqueous layer showed no further blue color. The aqueous layer was extracted with Et₂O and the combined organic layers were dried with MgSO₄. Removal of the solvent in vacuum and flash chromatography (PE-Et₂O, gradient elution from 4:1 to 1:1) of the crude product on SiO₂ provided 3-cyano-7-triiso-propylsilyloxy-4-methoxycarbazole (18) (yield 17.0 mg, 4%) as colorless crystals (mp 141-143 ˚C), then the diarylamine 16 (yield 28.2 mg, 7%) as colorless crystals, and, as the most polar fraction, 3-cyano-7-triisoprop-ylsilyloxy-2-methoxycarbazole (17) (yield 266.0 mg, 67%) as colorless crystals (mp 180-181 ˚C).

30 Olah GA. Narang SC. Gupta BGB. Malhotra R. J. Org. Chem.  1979,  44:  1247 

31 Bhatt MV. Kulkarni SU. Synthesis  1983,  249 

32 Winterfeldt E. Synthesis  1975,  617 

33 For a previous synthesis, see: Hsieh BR. Litt MH. Macromolecules  1985,  18:  1388 

34a Choi TA. Czerwonka R. Fröhner W. Krahl MP. Reddy KR. Franzblau SG. Knölker H.-J. ChemMedChem  2006,  1:  812 

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