Claudio Palomo et al.
COMMUNICATIONS
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Perkin Trans. 1 1981, 547–552; b) K. Matsumoto, A.
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Parlagh, L. Tçke, Tetrahedron; Asymmetry 2003, 14,
1917–1923; c) E. J. Corey, F. Y. Zhang, Org. Lett. 2000,
2, 4257–4259; d) D. Y. Kim, S. C. Huh, Tetrahedron
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ka, J. Am. Chem. Soc. 2004, 126, 11790–11791.
from smooth elaboration of the adducts into enan-
tioenriched g-nitro carboxylic acids and aldehydes.
Experimental Section
General Procedure for the Conjugate Addition of
Nitromethane to a’-Hydroxy Enones
Magnesium(II) triflate (32.2 mg, 0.10 mmol) and bisoxazo-
line 5 (42.8 mg, 0.12 mmol) were combined under a nitrogen
atmosphere and, after addition of nitromethane (3 mL,
55.56 mmol), the solution was stirred for 1 h at room tem-
perature. To this solution, molecular sieves (1.00 g, 4 or
3 ) were added and the resulting mixture was stirred for
an additional 1 h at the same temperature. The correspond-
ing a’-hydroxy enone (1 mmol) was then added at À208C or
room temperature and the resulting reaction mixture was
stirred at the given temperature for the time specified in
Table 2. The mixture was quenched with 1M HCl (3 mL),
diluted with CH2Cl2 and filtered through a glass filter
funnel. The organic layer was separated, and the aqueous
layer was extracted with CH2Cl2 (34 mL). The combined
organic layers were dried over MgSO4 and concentrated
under reduced pressure, and the residue was purified by
chromatography (silica gel; eluent: ethyl acetate/hexane,
1:4).
[7] Conjugate additions of carbamates: a) C. Palomo, M.
Oiarbide, R. Halder, M. Kelso, E. Gómez-Bengoa,
J. M. García, J. Am. Chem. Soc. 2004, 126, 9188–9189;
Friedel–Crafts reaction: b) C. Palomo, M. Oiarbide,
B. G. Kardak, J. M. García, A. Linden, J. Am. Chem.
Soc. 2005, 127, 4154–4155.
[8] Bases tested: triethylamine, diisopropylethylamine,
2,2,4,4-tetramethylpiperidine, and 2,6-di-tert-butylpyri-
dine.
[9] J. S. Johnson, D. A. Evans, Acc. Chem. Res. 2000, 33,
325–335.
Acknowledgements
This work was financially supported by The University of the
Basque Country (UPV/EHU), and Ministerio de Educación
y Ciencia (MEC, Spain). A predoctoral grant to R. P. from
UPV/EHU is acknowledged.
[10] Other magnesium salts, such as Mg
A
MgI2, and Mg(SbF6)2, led under identical conditions to
AHCTREUNG
negligible reaction conversions; MgCl2 was the excep-
tion, affording, after 6 days at À208C, product of 38%
ee (55% conversion).
[11] Homoaldol reaction: a) K. Juhl, N. Gathergood, K. A.
Jørgensen, Chem. Commun. 2000, 2211; Mannich reac-
tion: b) K. Juhl, N. Gathergood, K. A. Jørgensen,
Angew. Chem. Int. Ed. 2001, 40, 2995–2997; Henry re-
action: c) D. A. Evans, D. Seidel, M. Rueping, H. W.
Lam, J. T. Shaw, C. W. Downey, J. Am. Chem. Soc.
2003, 125, 12692–12693; Michael reaction: d) D. A.
Evans, R. J. Thomson, F. Franco, J. Am. Chem. Soc.
2005, 127, 10816–10817.
[12] For a recent paper wherein the basic character of mo-
lecular sieves is invoked, see: a) B. A. Steinhoff, A. E.
King, S. S. Stahl, J. Org. Chem. 2006, 71, 1861–1868;
for reviews on zeolites and molecular sieves see, for in-
stance: b) M. E. Davis, Acc. Chem. Res. 1993, 26, 111–
115; c) S. E. Sen, S. M. Smith, K. A. Sullivan, Tetrahe-
dron 1999, 55, 12657–12698;.
[13] The configuration of adducts 12a and 12h was deduced
from comparison with published data (see the Support-
ing Information for details). Assignments for the re-
maining adducts were made by analogy. Scission of ad-
ducts 11 is equally effective under the above conditions,
giving rise to the same compounds 12 and 13 along
with cyclohexanone.
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Adv. Synth. Catal. 2006, 348, 1161 – 1164