CHROMIUM(II) CHLORIDE REDUCTION OF a,b-UNSATURATED NITROALKENES.
A FACILE ROUTE TO CARBONYL COMPOUNDS.
Tetrahedron Letters,Vol.26,No.32,pp 3777-3778,(1985)
Although transformations of nitroparaffins or their salts to carbonyl compounds (the Nef reaction)(14) have been investigated extensively,(15) the readily accessible conjugated nitroalkenes have received little attention. (16-18) The present study may stimulate the use of low-valent transition metal species in the reduction of conjugated nitroalkenes analogous to their applications in the reduction of the corresponding nitroalkanes. (15c, l5d)
The following procedure is representative : chromium(II) chloride(20 mmol, 2.46 g)was placed in a nitrogen-flushed flask equipped with septum inlet and magnetic stirring bar.
Aqueous hydrochloric acid (3%, 30 mL) was injected into the flask followed by the slow addition of the b-nitrostyrene derivative (2 mmol, in 20 mL THF) at room temperature. A moderately exothermic reaction ensued. The mixture was refluxed for 4 hrs. and, after cooling, saturated with sodium chloride. The product was extracted into ether (3 x 30 mL) and worked up in the usual manner.
The crude carbonyl compound was purified using a silica gel column (ether/petroleum ether). The results are summarized in Table I.
TABLE I: CARBONYL COMPOUNDS FROM NITROALKENES VIA CHROMIUM(II) CHLORIDE REDUCTION
Nitroalkene(a) Product(b) Yield=[%] Ref
2-nitrostyrene Phenylacetaldehyde 80 15d
phenyl-2-nitropropene phenyl-2-propanone 81 4
p-bromo,P2NP p-bromo,P2P 79 4
3,4-diethoxy,P2NP 3,4-diethoxy,P2P 78 4
1-naphthalene-2-nitropropene 1-N-2-NP 72 4
(a)Prepared by the published procedure.(2)
(b)All products exhibited physical and spectral characteristics in accordance with the assigned structures. (c)Isolated and unoptimized yields.
REFERENCES AND NOTES
1. R. S. Varma and G. W. Kabalka, Synth. Commun., 14, 1093 (1984); Idem, Ibid, 15, 151 (1985).
2. M. S. Mourad, R. S. Varma and G. W. Kabalka, J. Org. Chem., 50, 133 (1985).
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4. M. S. Mourad, R. S. Varma and G. W. Kabalka, Synthesis, 000 (1985).
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7. R. S. Varma and G. W. Kabalka, Synth. Commun., 15, 000 (1985).
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11. S. Ranganathan and B. B. Singh, J. Chem. Soc. Chem. Commun., 218 (1970).
12. The reduction of l-nitrocyclohexene may have produced a significant quantity (-40%) of the corresponding 2-hydroxycyclohexanone.
13. It has been reported that chromous acetate generates carbonyl compounds from oximes which have been acetylated. {See E. J. Corey and J. E. Richman, J. Am. Chem. Soc., 92, 5276 (197O)}.
14. J. U. Nef, Justus Liebigs Ann. Chem., 280, 264 (1894).
15. For leading references see
(a) N. Kornblum, A. S. Erickson, W. J. Kelly and B. Henggeler, J. Org. Chem., 42, 4534 (1982);
(b) D. Seebach, E. W. Colvin, F. Lehr and T. Weller, Chimia, 33, 1 (1979)
(c) T.-L. Ho, Synthesis, 1 (1979);
(d) J. E. M&furry, Acc. Chem. Res., 7, 281 (1974); W. E. Noland, Chem. Rev., 55, 137 (1955) and references cited therein.
16. R. T. Gilsdorf and F. F. Nord, J. Am. Chem. Soc., 74, 1837 (1952).
17. A. B. B. Ferreira and K. Salisbury, J. Chem. Soc., Perkin Trans. II, 995 (1978).
l8. H. B. Hass, A. G. Susie and R. L. Heider, J. Org. Chem., 15, 8 (1950).
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