J. Szawkało et al. / Tetrahedron: Asymmetry 16 (2005) 3619–3621
3621
23
Figure 4. 1H NMRspectra (aromatic region) of (a) the racemic crispine A 1; (b) enriched in (+)-1 enantiomer, ½a ¼ þ77:3 (c 1, CHCl3) (Table 1,
D
23
D
entry 1); (c) (+)-1, ½a ¼ þ100:4 (c 1, CHCl3) (Table 1, entry 6) measured in the presence of (+)-(R)-10.
13. Hajipour, A. R.; Hantehzadeh, M. J. Org. Chem. 1999, 64,
8475–8478.
14. Szawkało, J.; Czarnocki, Z. Monatsh. Chem. 2005, 136,
1619–1627.
15. Uematsu, N.; Fujii, A.; Hashiguchi, S.; Ikariya, T.;
Noyori, R. J. Am. Chem. Soc. 1996, 118, 4916–4917.
16. According to the procedure given in Roszkowski, P.;
Wojtasiewicz, K.; Leniewski, A.; Maurin, J. K.; Lis, T.;
Czarnocki, Z. J. Mol. Catal. A: Chem. 2005, 232, 143–
149.
Therefore, the Ru-catalyzed asymmetric transfer hydro-
genation has again proven its extremely high efficiency
in the enantioselective synthesis of heterocyclic com-
pounds, allowing us to prepare crispine A in essentially
enantiopure form.
Acknowledgements
This work was supported by the Ministry of Science and
Information Society Technologies (Grant No. 3 T09A
073 28).
17. Typical procedure: The catalyst was pre-formed from
[RuCl2(C6H6)]2 (6 mg, 24 lmol) and (1S,2S)-1,2-diphenyl-
N-(p-toluoylsulfonyl)ethylenediamine 6 (7.3 mg, 20 lmol)
in 4 mL CH3CN. To a solution of enamine 5 (100 mg,
0.43 mmol) in CH3CN (10 mL) a 5:2 formic acid–trieth-
ylamine mixture (2.5mL) was introduced at 0 °C followed
by the addition of the pre-formed catalyst. The mixture
was then stirred at 0 °C for 10 h and then was made basic
by addition of aqueous Na2CO3 solution and extracted
with diethyl ether. The organic phase was dried (MgSO4)
and concentrated under reduced pressure. The residue was
purified by flash chromatography using 10:1 chloroform–
methanol as a solvent system to afford 90.8 mg (90%
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23
colourless oil; ½a ¼ þ100:4 (c 1, CHCl3), 1H NMR
D
(500 MHz, CDCl3): d 1.72 (m, 1H), 1.85 (m, 1H), 1.92 (m,
1H), 2.32 (m, 1H), 2.55 (q, 1H), 2.63 (m, 1H), 2.73 (m,
1H), 3.01 (m, 1H), 3.07 (m, 1H), 3.18 (m, 1H), 3.41 (t,
1H), 3.84 (s, 3H), 3.85 (s, 3H), 6.57 (s, 1H), 6.61 (s, 1H).
13C NMR(125 MHz, CDCl 3): d 22.21, 28.03, 30.45,
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130.93, 147.18, 147.30. ESMS (positive ion mode) m/z =
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23
18. For (+)-1, ½a ¼ þ100:4 (c 1, CHCl3), lit.1 for natural
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(+)-1 [a]D = +91 (MeOH). In our case a persistent
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