Hui Lv et al.
COMMUNICATIONS
30 min, was added ketene (1 mmol). The reaction mixture
was stirred at room temperature for 2 h. The reaction mix-
ture was then filtered through a pad of silica gel and washed
with ethyl acetate. The solvent was removed under reduced
pressure and the residue was purified by flash chromatogra-
phy on silica gel (petroleum ether/ethyl acetate, 30:1) to
give the desired product.
c) M. A. Calter, X. Guo, W. Liao, Org. Lett. 2001, 3,
1499; d) M. A. Calter, W. Liao, J. Am. Chem. Soc.
2002, 124, 13127; e) R. J. Duffy, K. A. Morris, D. Romo,
J. Am. Chem. Soc. 2005, 127, 16754; f) V. C. Purohit,
R. D. Richardson, J. W. Smith, D. Romo, J. Org. Chem.
2006, 71, 4549.
[5] For asymmetric reactions of disubstituted ketenes other
than dimerization, see: a) B. L. Hodous, J. C. Ruble,
G. C. Fu, J. Am. Chem. Soc. 1999, 121, 2637; b) E. C.
Lee, B. L. Hodous, E. Bergin, C. Shih, G. C. Fu, J. Am.
Chem. Soc. 2005, 127, 11586; c) C.-Y. Li, X.-L. Sun, Q.
Jing, Y. Tang, Chem. Commun. 2006, 2980.
[6] For the reviews of NHC-catalyzed reactions, see: a) D.
Enders, O. Niemeier, A. Henseler, Chem. Rev. 2007,
107, 5606; b) N. Marion, S. Diez-Gonzalez, S. P. Nolan,
Angew. Chem. 2007, 119, 3046; Angew. Chem. Int. Ed.
2007, 46, 2988; c) K. Zeitler, Angew. Chem. 2005, 117,
7674; Angew. Chem. Int. Ed. 2005, 44, 7506; d) M.
Christmann, Angew. Chem. 2005, 117, 2688; Angew.
Chem. Int. Ed. 2005, 44, 2632; e) D. Enders, T. Balen-
siefer, Acc. Chem. Res. 2004, 37, 534.
ACHTUNGTRENNUNG(S,Z)-3-Ethyl-3-phenyl-4-(1-phenylpropylidene)oxetan-2-
one (2a): Yield: 129.4 mg (83%); Rf =0.68 (petroleum ether/
ethyl acetate=20:1); colorless oil; [a]2D5: À23.7 (c 2.05,
CHCl3). 1H NMR (300 MHz, CDCl3): d=7.17–7.41 (m,
10H), 2.23–2.34 (m, 3H), 2.05–2.22 (m, 1H), 1.13 (t, J=
7.5 Hz, 3H), 0.81 (t, J=7.5 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d=170.8, 143.9, 135.3, 134.6, 129.2, 128.5, 128.5,
128.1, 127.5, 126.4, 116.4, 70.0, 26.2, 22.8, 12.7, 9.9; IR (KBr,
film): v=2969, 1857, 1140, 914, 889, 696 cmÀ1; HR-MS-EI:
m/z=292.1467 [M+], calcd. for C20H20O2: 292.1463. HPLC
analysis: 96% ee, [Daicel CHIRALPAK AD-H column;
208C; 0.5 mLminÀ1; solvent system: 2-propanol/hexane=
5:95; retention times: 8.6 min (minor), 10.3 min (major)].
[7] a) Y.-R. Zhang, L. He, X. Wu, P.-L. Shao, S. Ye, Org.
Lett. 2008, 10, 277; b) Y.-R. Zhang, H. Lv, D. Zhou, S.
Ye, Chem. Eur. J. 2008, 14, 8473.
Acknowledgements
[8] Smith et al. have simultaneously reported their results
of the NHC-catalyzed formal cycloaddition of disubsti-
tuted ketenes with imines: N. Duguet, C. D. Campbell,
A. M. Z. Slawin, A. D. Smith, Org. Biomol. Chem.
2008, 6, 1108.
We are grateful for the financial support from Chinese Acad-
emy of Sciences and Natural Sciences Foundation of China
(No. 20602036).
[9] Enders et al. have simultaneously reported the synthe-
sis of NHC precursor 3a, b from l-pyroglutamic acid:
D. Enders, J. Han, Tetrahedron: Asymmetry. 2008, 19,
1367.
[10] a) L. He, Y.-R. Zhang, X.-L. Huang, S. Ye, Synthesis
2008, 2825; b) L. He, T.-Y. Jian, S. Ye, J. Org. Chem.
2007, 72, 7466.
[11] CCDC 699375 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic
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Adv. Synth. Catal. 2008, 350, 2715 – 2718