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7 For previous work on the enantioselective addition of nitroalkanes
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Hojabri, A. Hartikka, F. M. Moghaddam and P. I. Arvidsson,
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M. Huttl, C. Grondal and G. Raabe, Nature, 2006, 441, 861; recent
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Vera, Angew. Chem., Int. Ed., 2007, 46, 8431; H. Gotoh, H.
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2660.
Scheme 2 Synthetic route for the preparation of the optically active
(R)-baclofen hydrochloride salt.
1–2 mol% loading level for the catalyst. The results indicated
that this methodology might be of practical and general utility
for the synthetic community. Further investigations of the
mechanism of this methodology are currently ongoing and
results from which will be presented in due course.
8 For a highlight related to diarylprolinol ethers, see: C. Palomo and
A. Mielgo, Angew. Chem., Int. Ed., 2006, 45, 7876.
9 For recent examples on conjugate addition with an iminium
mechanism using diarylprolinol ethers as an organocatalyst, see:
M. Marigo, T. Schulte, J. Franzen and K. A. Jørgensen, J. Am.
Chem. Soc., 2005, 127, 15710; S. Brandau, A. Landa, J. Franzen,
M. Marigo and K. A. Jørgensen, Angew. Chem., Int. Ed., 2006, 45,
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10 For a report on using NaOAc as a basic additive in iminium-based
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11 An example with DABCO as a basic additive in the organocata-
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12 S. Brandau, A. Landa, J. Franzen, M. Marigo and K. A. Jørgen-
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Notes and references
z General procedure for the Michael addition of nitroalkanes to a,b-
unsaturated aldehydes: to a mixed solution of 1 : 9 CH2Cl2–MeOH
(v/v, 2.0 mL) was added a,b-unsaturated aldehyde 1 (1.0 mmol),
nitroalkane 2 (3.0 mmol), catalyst 4 (6.5 mg, 0.02 mmol) and lithium
acetate (6.6 mg, 0.10 mmol). The reaction mixture was stirred at room
temperature for the time indicated in Table 2 and then the solvent was
removed under vacuum. Water (5.0 mL) was added to the residue and
it was extracted with CH2Cl2 three times. The combined organic
phases were dried over anhydrous Na2SO4, filtered and evaporated
under vacuum. The residue was purified by column chromatography
on silica gel (350–400 mesh) to yield the desired addition product.
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1234 | Chem. Commun., 2008, 1232–1234