Synlett 2004(8): 1343-1346  
DOI: 10.1055/s-2004-825614
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Stereoselective Entry to Tetrasubstituted Quinolizidines and the Puzzling Structural Assignment of the Lupin Alkaloid Plumerinine

Adriano O. Maldaner, Ronaldo A. Pilli*
Instituto de Química, Unicamp P.O. Box 6154 13084-971 Campinas, SP Brazil
Fax: +55(19)37883023; e-Mail: pilli@iqm.unicamp.br;
Further Information

Publication History

Received 1 March 2004
Publication Date:
18 May 2004 (online)

Abstract

A thermodynamically controlled stereoselective synthesis of quinolizidinone (+/-)-13 via α-amidoalkylation of an intermediate N-acyliminium ion derived from α-ethoxy piperidine 9, followed by intramolecular Michael addition is described. Based on their NMR data, quinolizidine alcohols 14 and 15 were ruled out as possible structures of the lupin alkaloid plumerinine.

10

Preparation of (4 SR ,6 RS ,9 RS ,9 aRS )-4-isopropyl-6,9-dimethyl quinolizidin-2-one(13):
To a CH2Cl2 (3.0 mL) solution of piperidinone 9 (0.032 g, 0.10 mmol) at 0 °C was added TFA (0.110 g, 1.00 mmol). The mixture was stirred 3 h at r.t., quenched with sat. aq NaHCO3 (3.0 mL) and extracted with CH2Cl2 (4 × 5 mL). The residue was taken up in MeOH (3.0 mL) containing 30% aq NH3 (3.0 mL) and heated at 60 °C for 24 h. After extraction with CH2Cl2 (5 × 15 mL), the organic phase was dried over anhyd MgSO4 and evaporated to afford a residue, which was chromatographed on silica gel (9:1 hexanes-EtOAc) to afford 0.0054 g (0.03 mmol, 30% yield) of quinolizidinone 13. IR (film): 2956, 2925, 2873, 2854, 1709, 1464, 1336, 1260, 1078 cm-1. 1H NMR (500 MHz, CDCl3): δ = 3.12 (dt, J = 12.5, 3.8 Hz, 1 H), 2.96 (ddd, J = 9.7, 6.4, 1.7 Hz, 1 H), 2.85 (m, 1 H), 2.51 (dd, J = 14.0, 6.6 Hz, 1 H), 2.45 (br d, J = 14.0 Hz, 1 H), 2.35 (dt, J = 14.0, 1.8 Hz, 1 H), 2.02 (ddd, J = 14.0, 2.9, 1.9 Hz, 1 H), 1.96 (m, 1 H), 1.68 (dq, J = 12.8, 6.6 Hz, 1 H), 1.64 (m, 1 H), 1.50 (dq, J = 11.7, 7.0 Hz, 1 H), 1.38 (m, 1 H), 1.26 (m, 1 H), 1.07 (d, J = 5.9 Hz, 3 H), 0.91 (d, J = 6.6 Hz, 3 H), 0.89 (d, J = 6.6 Hz, 3 H), 0.82 (d, J = 7.0 Hz, 3 H).13C NMR (125.7 MHz, CDCl3): δ = 211.6, 62.7, 56.7, 46.7, 38.3, 36.4, 35.7, 34.1, 28.8, 27.5, 21.2, 20.7, 19.8, 18.5. HRMS (EI): m/z calcd for C11H18NO [M+ - C3H7]: 180.1388. Found: 180.1387.

13

The experimental conditions employed in this work for the intramolecular Michael reaction (aq NH3, MeOH, 60 °C) were previously used to carry out epimerization in quinolizidinone and indolizidinone systems (see ref. 8).

14

Data for 14: IR (film): 3384, 2956, 2925, 2871, 2855, 1461, 1374, 1260, 1089, 1071, 1047, 1031 cm-1. 1H NMR (500 MHz, CDCl3): δ = 4.18 (m, 1 H), 3.22 (m, 1 H), 2.78 (m, 1 H), 2.50 (m, 1 H), 2.20 (m, 1 H), 1.99 (td, J = 13.2, 4.5 Hz, 1 H), 1.65-1.80 (m, 3 H), 1.60 (m, 2 H), 1.10-1.50 (m, 4 H), 0.99 (t, J = 5.8 Hz, 3 H), 0.92 (t, J = 6.6 Hz, 6 H), 0.82 (d, J = 7.1 Hz, 3 H). 13C NMR (125 MHz, CDCl3): δ = 66.7, 59.3, 50.1, 47.4, 36.0, 34.0, 30.1, 27.6, 26.9, 25.3, 21.2, 21.1, 20.4, 18.6. HRMS (EI): m/z calcd for C14H27NO: 225.2093. Found: 225.2092.
Data for 14·HCl: IR (KBr): 3334, 2963, 2875, 2709, 1464, 1455, 1066 cm-1. 1H NMR (500 MHz, D2O): δ = 4.25 (quint, J = 4.4 Hz, 1 H), 3.91 (dt, J = 13.4, 4.1 Hz, 1 H), 3.71 (m, 1 H), 3.42 (m, 1 H), 2.59 (m, 1 H), 2.36 (ddd, J = 15.6, 13.4, 5.1 Hz, 1 H), 2.18 (m, 1 H), 2.10 (m, 1 H), 1.94-2.04 (m, 2 H), 1.74-1.88 (m, 2 H), 1.50-1.65 (m, 2 H), 1.37 (d, J = 6.3 Hz, 3 H), 1.08 (d, J = 6.7 Hz, 3 H), 1.07 (d, J = 6.7 Hz, 3 H), 0.98 (d, J = 7.1 Hz, 3 H). 13C NMR (125.7 MHz, D2O): δ = 64.8, 62.8, 55.8, 53.9, 32.6, 31.8, 29.0, 25.8, 25.0, 24.9, 19.7, 19.1, 17.5, 17.1.
Data for 15: IR (film): 3345, 2954, 2926, 2870, 1463, 1366, 1260, 1084, 1058, 1024 cm-1. 1H NMR (500 MHz, CDCl3): δ = 3.83 (m, 1 H), 2.80 (m, 2 H), 2.61 (m, 1 H), 1.75-1.90 (m, 3 H), 1.50-1.60 (m, 2 H), 1.30-1.45 (m, 3 H), 1.20-1.30 (m, 3 H), 0.95 (d, J = 5.8 Hz, 3 H), 0.89 (d, J = 6.6 Hz, 3 H), 0.88 (t, J = 6.6 Hz, 3 H), 0.84 (J = 7.1 Hz, 3 H). 13C NMR (125 MHz, CDCl3): δ = 67.5, 60.4, 53.9, 46.1, 36.3, 34.5, 28.6, 28.1, 27.2, 27.1, 21.4, 20.9, 20.8, 18.9. HRMS (EI): m/z calcd for C14H27NO: 225.2093. Found: 225.2092.
Data for 15·HCl: 1H NMR (500 MHz, D2O): δ = 3.99 (m, 1 H), 3.78 (m, 1 H), 3.65 (dt, J = 13.2, 3.6 Hz, 1 H), 3.32 (ddd, J = 10.1, 5.1, 2.5 Hz, 1 H), 2.11 (m, 1 H), 1.85-2.05 (m, 3 H), 1.81 (m, 1 H), 1.58-1.73 (m, 3 H), 1.35-1.48 (m, 2 H), 1.17 (d, J = 6.4 Hz, 3 H), 0.89 (d, J = 6.4 Hz, 3 H), 0.88 (d, J = 6.4 Hz, 3 H), 0.78 (d, J = 6.8 Hz, 3 H).