Synlett 2008(4): 525-528  
DOI: 10.1055/s-2008-1032091
LETTER
© Georg Thieme Verlag Stuttgart · New York

Highly Efficient Domino Reaction for the Synthesis of the Erythrina and B-Homoerythrina Alkaloid Skeleton

Lutz F. Tietze*, Nina Tölle, Claudia Noll
Institut für Organische und Biomolekulare Chemie, Georg-August-Universität, Tammannstr. 2, 37077 Göttingen, Germany
Fax: +49(551)399476; e-Mail: ltietze@gwdg.de;
Further Information

Publication History

Received 28 October 2007
Publication Date:
12 February 2008 (online)

Abstract

A Lewis acid catalyzed domino-amidation-spirocyclization reaction is described which provides the spirocyclic core of the erythrina and B-homoerythrina alkaloids, forming three bonds in one process.

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General Procedure
To a stirred solution of amine 2 (1.00 equiv) in MeCN (0.5 mL/mmol) was added dropwise at 0 °C AlMe3 (2.00 M in toluene, 2.00 equiv), then In(OTf)3 (4-25 mol%) and the ester 3 (1.00 equiv), and stirring was continued for 3-17 h at r.t. or the mixture was heated to 100-180 °C under microwave irradiation. The reaction mixture was cooled to 0 °C, TfOH (3.5 equiv) was added dropwise and stirring was continued for 5 h at r.t. Subsequently, the mixture was quenched by addition of sat. aq NaHCO3 at 0 °C with stirring for 20 min. The mixture was extracted with EtOAc, the combined organic layers were washed with brine, dried over Na2SO4, and the solvent was removed under reduced pressure. The crude product was subjected to column chromatography to yield 38-99% of the spirocycle 4.
Compound 4a: 1H NMR (300 MHz, DMSO): d = 1.35-1.60 (m, 5 H, 3-H2, 2-H2, 1-Ha), 1.75-1.82 (m, 2 H, 4-H2), 1.95-1.99 (m, 1 H, 1-Hb), 2.12 (mc, 2 H, 7-H2), 2.54-2.60 (m, 1 H, 6-H), 2.63 (ddd, J = 3.0, 6.0, 16.5 Hz, 1 H, 11-Ha), 2.80 (ddd, J = 7.4, 10.0, 16.5 Hz, 1 H, 11-Hb), 3.15 (ddd, J = 6.0, 10.0, 13.2 Hz, 1 H, 10-Ha), 3.71 (s, 3 H, OCH3), 3.76 (s, 3 H, OCH3), 3.86 (ddd, J = 3.0, 7.4, 13.2 Hz, 1 H, 10-Hb), 6.67 (s, 1 H, 17-H), 6.91 (s, 1 H, 14-H). 13C NMR (300 MHz, DMSO): d = 20.06 (C-2), 20.57 (C-3), 26.14 (C-11), 27.17 (C-1), 34.26 (C-10), 35.01 (C-4), 36.29 (C-7), 36.67 (C-6), 55.42 (OCH3), 55.74 (OCH3), 61.75 (C-5), 108.7 (C-14), 112.5 (C-17), 125.5 (C-12), 134.7 (C-13), 147.0 (C-16), 147.5 (C-15), 173.6 (C-8).
Compound 4b: 1H NMR (300 MHz, DMSO): d = 1.18-1.42 (m, 2 H, 11-Ha, 13*-Ha), 1.42-1.69 (m, 5 H, 2-H2, 12*-H2, 13*-Hb), 1.69-1.82 (m, 2 H, 1-H2), 2.05 (dd, J = 18.5, 6.2 Hz, 1 H, 14-Ha), 2.18-2.26 (m, 1 H, 11-Hb), 2.33-2.47 (m, 1 H, 14-Hb), 2.52 (d, J = 5.9 Hz, 1 H, 6-Ha), 2.63 (mc, 1 H, 14a-H), 2.84-2.99 (m, 1 H, 6-Hb), 3.19 (td, J = 12.3, 5.9 Hz, 1 H, 5-Ha), 3.70 (s, 3 H, OCH3), 3.73 (s, 3 H, OCH3), 4.53 (dd, J = 13.2, 7.5 Hz, 1 H, 5-Hb), 6.62 (s, 1 H, 7-H), 6.82 (s, 1 H, 10-H). 13C NMR (300 MHz, DMSO): d = 21.42 (C-13*), 22.15 (C-12*), 25.07 (C-1), 25.60 (C-2), 26.06 (C-6), 28.14 (C-14), 34.48 (C-5), 34.77 (C-14a), 39.58 (C-11), 55.32 (OCH3), 55.89 (OCH3), 60.99 (C-10b), 107.2 (C-10), 112.9 (C-7), 126.5 (C-6a), 135.8 (C-10a), 146.9 (C-9), 147.4 (C-8), 171.0 (C-3).
Compound 4c: 1H NMR (300 MHz, DMSO): d = 1.28-1.48 (m, 3 H, 3-H2, 1-Ha), 1.49-1.58 (m, 2 H, 2-H2), 1.71-1.75 (m, 1 H, 4-Ha), 1.78-1.83 (m, 1 H, 4-Hb), 1.91-1.99, (m, 1 H, 1-Hb), 2.09-2.14 (m, 2 H, 7-H2), 2.49-2.54 (m, 1 H, 6-H), 2.59-2.67 (m, 1 H, 11-Ha), 2.73-2.87 (m, 1 H, 11-Hb), 3.11-3.21 (m, 1 H, 10-Ha), 3.78-3.85 (m, 1 H, 10-Hb), 5.94 (s, 2 H, 18-H2), 6.65 (s, 1 H, 17-H), 6.97 (s, 1 H, 14-H). 13C NMR (300 MHz, DMSO): d = 19.90 (C-2), 20.49 (C-3), 26.58 (C-11), 27.02 (C-1), 34.25 (C-10), 35.01 (C-4), 36.22 (C-7), 36.71 (C-6), 62.13 (C-5), 100.7 (C-18), 104.9 (C-14), 108.7 (C-17), 126.8 (C-12), 135.9 (C-13), 145.6 (C-16), 145.7 (C-15), 173.6 (C-8).
Compound 4d: 1H NMR (300 MHz, DMSO): d = 1.20-1.35 (m, 2 H, 11-Ha, 13*-Ha), 1.35-1.52 (m, 2 H, 1-H2), 1.50-1.80 (m, 5 H, 2-H2, 12*-H2, 13*-Hb), 2.04 (dd, J = 18.6, 6.6 Hz, 1 H, 14-Ha), 2.18-2.25 (m, 1 H, 11-Hb), 2.32-2.44 (m, 1 H, 14-Hb), 2.55-2.70 (m, 2 H, 6-Ha, 14a-H), 2.80-2.92 (m, 1 H, 6-Hb), 3.14 (td, J = 11.9, 5.8 Hz, 1 H, 5-Ha), 4.52 (dd, J = 13.7, 7.4 Hz, 1 H, 5-Hb), 5.96 (s, 2 H, OCH2O), 6.61 (s, 1 H, 7-H), 6.92 (s, 1-H, 10-H).13C NMR (300 MHz, DMSO): d = 21.36 (C-13*), 22.07 (C-12*), 25.05 (C-1), 25.56 (C-2), 26.53 (C-6), 28.10 (C-14), 34.22 (C-5), 34.83 (C-14a), 39.62 (C-11), 61.12 (C-10b), 100.5 (OCH2O), 103.3 (C-10), 109.1 (C-7), 127.6 (C-6a), 137.0 (C-10a), 145.4 (C-9), 145.5 (C-8), 170.8 (C-3).
Compound 4e: 1H NMR (300 MHz, DMSO): d = 1.48-1.64 (m, 6 H, 11-Ha, 10-H2, 9-H2, 8-Ha), 1.82-1.87 (m, 1 H, 11-Hb), 1.94-1.99 (m, 1 H, 8-Hb), 2.10-2.19 (m, 2 H, 4-Ha, 8a-H), 2.39-2.48 (m, 1 H, 4-Hb), 2.48-2.74 (m, 2 H, 12-H2), 2.96 (td, J = 12.3, 6.7 Hz, 1 H, 5-Ha), 4.00-4.11 (qd, 1 H, J = 6.5, 1.3 Hz, 5-Hb), 6.85 (d, J = 5.4 Hz, 1 H, 3-H), 7.35 (d, J = 5.4 Hz, 1 H, 2-H). 13C NMR (300 MHz, DMSO): d = 19.57 (C-10), 21.00 (C-9), 24.46 (C-11), 25.10 (C-12), 33.16 (C-5), 34.43 (C-8), 34.54 (C-4), 40.33 (C-8a), 61.03 (C-12a), 122.9 (C-2), 126.9 (C-3), 132.4 (C-12b), 139.2 (C-3a), 171.0 (C-7).
Compound 4f: 1H NMR (300 MHz, DMSO-d 6): d = 1.35-1.61 (m, 4 H, 12-Ha, 13-H2, 12-Hb), 1.61-1.80 (m, 4 H, 10-H2, 9-Ha, 11-Ha), 1.84-1.94 (m, 2 H, 11-Hb), 2.03-2.09 (m, 1 H, 9a-H), 2.11-2.25 (m, 2 H, 8-Ha, 9-Hb), 2.37-2.49 (m, 1 H, 8-Hb), 2.53 (ddd, J = 1.0, 5.3, 16.5 Hz, 1 H, 4-Ha), 2.70 (ddd, J = 6.8, 11.7, 16.5 Hz, 1 H, 4-Hb), 3.16 (ddd, J = 5.3, 11.7, 13.3 Hz, 1 H, 5-Ha), 4.58 (ddd, J = 1.0, 6.8, 13.3 Hz, 1 H, 5-Hb), 6.80 (d, J = 5.0 Hz, 1 H, 3-H), 7.34 (d, J = 5.0 Hz, 1 H, 2-H). 13C NMR (75 MHz, DMSO-d 6): d = 21.69 (C-12), 22.77 (C-10), 23.10 (C-13), 24.30 (C-4), 26.82 (C-11), 29.68 (C-8), 34.88 (C-5), 38.20 (C-9), 39.34 (C-9a), 61.27 (C-13a), 122.8 (C-2), 127.3 (C-3), 134.3 (C-3a), 142.1 (C-13b), 170.2 (C-7).
Compound 4g: 1H NMR (300 MHz, DMSO-d 6): d = 1.46-1.68 (m, 6 H, 5-H2, 6-H2, 7-Ha, 4-Ha), 1.85-2.99 (m, 2 H, 7-Hb, 4-Hb), 2.14 (dd, J = 6.9, 14.0 Hz, 8-Ha), 2.21-2.29 (m, 1 H, 7a-H), 2.35 (ddd, J = 0.8, 8.9, 14.0 Hz, 1 H, 8-Hb), 2.70-2.86 (m, 2 H, 12-H2), 3.01-3.11 (m, 1 H, 11-Ha), 4.09-4.16 (m, 1 H, 11-Hb), 7.18 (d, J = 5.3 Hz, 1 H, 3-H), 7.35 (d, J = 5.3 Hz, 1 H, 2-H). 13C NMR (75 MHz, DMSO-d 6): d = 19.95 (C-5), 20.23 (C-6), 23.88 (C-12), 24.97 (C-7), 33.45 (C-11), 34.12 (C-4), 35.08 (C-8), 37.68 (C-7a), 61.10 (C-3b), 123.4 (C-2), 124.3 (C-3), 132.3 (C-12a), 140.8 (C-3a), 171.9 (C-9).
Compound 4h: 1H NMR (300 MHz, DMSO-d 6): d = 1.21-1.38 (m, 1 H, 4-Ha), 1.38-1.55 (m, 4 H, 4-Hb, 8-H2, 6-Ha), 1.55-1.68 (m, 2 H, 5-H2), 1.68-1.78 (m, 2 H, 7-H2), 2.09 (mc, 1 H, 9-Ha), 2.17-2.24 (m, 1 H, 6-Hb), 2.37-2.47 (m, 2 H, 7a-H, 9-Hb), 2.63 (dd, J = 5.3, 16.2 Hz, 1 H, 13-Ha), 2.90 (ddd, J = 6.9, 11.7, 16.2 Hz, 1 H, 13-Hb), 3.23 (ddd, J = 5.3, 11.7, 13.2 Hz, 1 H, 12-Ha), 4.58 (dd, J = 6.9, 13.2 Hz, 1 H, 12-Hb), 7.00 (d, J = 5.4 Hz, 1 H, 3-H), 7.27 (d, J = 5.4 Hz, 1 H, 2-H). 13C NMR (75 MHz, DMSO-d 6): d = 21.35 (C-4), 22.78 (C-8), 23.06 (C-13), 24.69 (C-7), 25.76 (C-5), 28.67 (C-9), 35.06 (C-12), 36.46 (C-7a), 38.31 (C-6), 61.42 (C-3b), 122.7 (C-3), 123.2 (C-2), 134.1 (C-13a), 143.21 (C-3a), 171.3 (C-10).