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Synlett 2004(4): 615-618  
DOI: 10.1055/s-2004-817753
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Novel Approach to Erythrinan Alkaloids by Utilizing Substituted Biphenyl as Building Block

Yoshizumi Yasui, Yukiko Koga, Keisuke Suzuki, Takashi Matsumoto*
Department of Chemistry, Tokyo Institute of Technology and CREST-JST Agency, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8551, Japan
Fax: +81(3)5734-3531; e-Mail: tmatsumo@chem.titech.ac.jp;
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Publikationsverlauf

Received 28 December 2003
Publikationsdatum:
10. Februar 2004 (online)

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Abstract

Aryl ortho-quinone monoacetal 6 possessing a carbamate group on the side chain was synthesized from the appropriate biphenyl precursor via selective oxidation of one of the aromatic rings. Under Lewis acidic conditions, the carbamate group underwent internal attack at the quinone acetal moiety to give the spiro tricycle 9 corresponding to the A-, C-, and D-rings of erythrinan ­alkaloids, from which O-methylerysodienone was synthesized via the B ring formation in an efficient manner.

Key words

erythrinan alkaloid - biphenyl compound - spirocyclization - ortho-quinone acetal - O-methylerysodienone

7

All new compounds were fully characterized by 1H and 13C NMR, IR and combustion analysis. Data for the selected compounds follow. Compound 5: Colorless needles (hexane), mp 99.5-100.0 °C. 1H NMR (CDCl3): δ = 7.48 (d, 2 H, J = 7.4 Hz), 7.39 (dd, 2 H, J 1 = J 2 = 7.4 Hz), 7.32 (dd, 1 H, J 1 = J 2 = 7.4 Hz), 6.90 (s, 1 H), 6.79 (s, 1 H), 6.66 (s, 1 H), 6.63 (s, 1 H), 5.17 (s, 2 H), 4.39 (br s, 1 H), 3.92 (s, 3 H), 3.85 (s, 3 H), 3.82 (s, 3 H), 3.61-3.50 (m, 2 H), 3.26-3.09 (m, 2 H), 2.59-2.40 (m, 4 H), 1.40 (s, 9 H), 0.95 (s, 21 H). 13C NMR (CDCl3): δ = 155.7, 148.1, 147.5, 147.1, 146.9, 137.1, 133.5, 132.9, 129.0, 128.9, 128.5, 127.8, 127.4, 115.7, 113.7, 113.2, 112.1, 79.1, 71.0, 64.0, 56.1, 55.9, 55.8, 41.4, 36.6, 33.0, 28.3, 17.9, 11.8. IR (KBr): 3330, 2940, 2865, 1700, 1685, 1510, 1465, 1250, 1160, 1115 cm-1. Anal. Calcd for C40H59NO7Si: C, 69.23; H, 8.57; N, 2.02. Found: C, 69.39; H, 8.87; N, 1.93. Compound 6: 1H NMR (CDCl3): δ = 6.77 (s, 1 H), 6.62 (s, 1 H), 6.21 (s, 1 H), 6.05 (s, 1 H), 4.59 (br, 1 H), 3.91 (s, 3 H), 3.85 (s, 3 H), 3.68-3.58 (m, 2 H), 3.41 (s, 3 H), 3.40 (s, 3 H), 3.40-3.19 (m, 2 H), 2.71 (ddd, 1 H, J 1 = J 2 = 6.4 Hz, J 3 = 12.8 Hz), 2.50 (ddd, 1 H, J 1 = J 2 = 6.4 Hz, J 3 = 12.8 Hz), 2.27 (ddd, 1 H, J 1 = J 2 = 7.2 Hz, J 3 = 14.5 Hz), 2.19 (ddd, 1H, J 1 = J 2 = 7.2 Hz, J 3 = 14.5 Hz), 1.42 (s, 9 H), 0.97 (s, 21 H). 13C NMR (CDCl3): δ = 193.9, 155.7, 152.6, 148.8, 147.4, 139.7, 133.4, 129.3, 129.0, 124.3, 112.2, 112.1, 91.1, 79.3, 61.1, 55.9, 55.8, 49.9, 49.8, 41.3, 37.3, 33.4, 28.4, 17.9, 11.8. IR (NaCl): 3380, 2940, 2870, 1710, 1680, 1515, 1465, 1365, 1250, 1230, 1170, 1100, 755 cm-1. Anal. Calcd for C34H55NO8Si: C, 64.42; H, 8.75; N, 2.21. Found: C, 64.24; H, 8.98; N, 2.01. Compound 9: 1H NMR (CDCl3): δ = 6.61 (s, 1 H), 6.45 (s, 1 H), 6.19 (s, 1 H), 5.79 (s, 1 H), 4.34 (ddd, 1 H, J 1 = J 2 = 4.1 Hz, J 3 = 12.9 Hz), 3.86 (s, 3 H), 3.70-3.63 (m, 1 H), 3.67 (s, 3 H), 3.65 (s, 3 H), 3.47 (ddd, 1 H, J 1 = 6.2 Hz, J 2 = 8.5 Hz, J 3 = 10.9 Hz), 3.36 (ddd, 1 H, J 1 = 5.8 Hz, J 2 = 8.7 Hz, J 3 = 10.9 Hz), 3.01 (ddd, 1 H, J 1 = 4.1 Hz, J 2 = 10.9 Hz, J 3 = 15.3 Hz), 2.80 (ddd, 1 H, J 1 = 3.1 Hz, J 2 = 4.1 Hz, J 3 = 15.3 Hz), 2.40 (ddd, 1 H, J 1 = 5.8 Hz, J 2 = 8.5 Hz, J 3 = 11.6 Hz), 2.08 (ddd, 1 H, J 1 = 6.2 Hz, J 2 = 8.7 Hz, J 3 = 11.6 Hz), 1.35 (s, 9 H), 0.96 (s, 21 H). 13C NMR (CDCl3): δ = 181.7, 165.8, 155.0, 149.7, 148.5, 147.9, 128.5, 123.9, 123.5, 118.3, 111.2, 109.7, 81.6, 63.9, 61.3, 55.9, 55.8, 55.0, 40.2, 34.0, 29.2, 28.1, 17.8, 11.7. IR (NaCl): 2940, 2865, 1695, 1670, 1645, 1620, 1515, 1465, 1365, 1260, 1220, 1160, 1090, 755 cm-1. Anal. Calcd for C33H51NO7Si: C, 65.86; H, 8.54; N, 2.33. Found: C, 65.59; H, 8.58; N, 2.05. Compound 12: Pale yellow needles (CHCl3), mp 157.5-158.0 °C. 1H NMR (CDCl3): δ = 6.57 (s, 1 H), 6.38 (s, 1 H), 6.31 (s, 1 H), 5.99 (s, 1 H), 3.85 (s, 3 H), 3.70 (s, 3 H), 3.62 (s, 3 H), 3.53 (ddd, 1 H, J 1 = 5.7 Hz, J 2 = 12.3 Hz, J 3 = 14.4 Hz), 3.32 (ddd, 1 H, J 1 = J 2 = 7.0 Hz, J 3 = 14.4 Hz), 3.31-3.14 (m, 3 H), 2.71-2.59 (m, 2 H), 2.54 (dd, 1 H, J 1 = 5.7 Hz, J 2 = 17.3 Hz). 13C NMR (CDCl3):
δ = 181.7, 167.3, 149.7, 148.5, 148.0, 125.9, 124.1, 122.4, 115.7, 112.1, 108.3, 64.8, 55.83, 55.82, 55.0, 47.0, 40.9, 27.9, 20.2. IR (KBr): 2940, 2845, 1675, 1655, 1620, 1510, 1465, 1250, 1210, 1175, 1105, 1010 cm-1. Anal. Calcd for C19H21NO4: C, 69.71; H, 6.47; N, 4.28. Found: C, 69.41; H, 6.76; N, 4.04.

9

Boronic acid 2 was prepared from isovanillin in six steps [(1) BnBr, NaOH aq, Bu4NHSO4, CH2Cl2 (73%); (2) Ph3P=CH2, THF (98%); (3) (sia)2BH, THF, then H2O2, NaOH aq (97%); (i-Pr)3SiCl, imidazole, DMF (quant); (5) NBS, DMF (84%); (6) BuLi, THF, -78 °C, then B(i-PrO)3, -78 °C to 0 °C, then 2 M HCl aq (75%)].

12

Compound 7 was synthesized from aryl bromide i and boronic acid ii in three steps [(1) 10 mol% Pd(PPh3)4, Ba(OH)2, DME, H2O, reflux; (2) H2, 10% Pd/C, MeOH; (3) (AcO)2IPh, MeOH] in 37% overall yield (Figure [2] ).

13

Experimental Procedure as Follows: To a mixture of powdered molecular sieves 4 Å (40 mg) and BF3·OEt2 (2.6 mg, 18 µmol) in CH2Cl2 (0.5 mL) was added 6 (49.2 mg, 0.0776 mmol) in CH2Cl2 (1.5 mL) at -20 °C. After 40 min, the reaction was quenched with sat. aq NaHCO3 and the mixture was extracted with EtOAc (× 3). The combined organic extracts were washed with brine, dried (Na2SO4), and concentrated in vacuo. The residue was purified by PTLC (hexane/EtOAc = 6:4) to give 9 (39.3 mg, 84%) as a colorless oil.

14

Cu(OTf)2, Sc(OTf)3, and Yb(OTf)3, though worked satisfactorily, did not exceed BF3·OEt2 in the yield of 9.