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Organic syntheses vol 58 - Sheppard W.A.

Sheppard W.A., Buchi G.H. Organic syntheses vol 58 - Wiley, 1978. - 123 p.
Download (direct link): organicsynthesesvol581978.pdf
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3. Discussion
This procedure has been shown2 to be extremely general and
applicable to a wide variety of straight-chain 1-acetylenes, 4-substituted 1-acctylenes, and a,a>-diacetylenes, together with primary halides, sterically hindered primary halides, secondary halides, and a,&>-dihalides.
Most of the compounds formed are new and were formerly inaccessible,7 being only available by dehydrohalogenation of gem-inal or 1,2-dibromides which are often unavailable themselves.7 Alcoholic potassium hydroxide8'9 or sodamide in liquid paraffin7-10 under forceful conditions has been used for this elimination, but yields are generally not good.7-10
The procedure described here is characterized by good yields, mild conditions, and easy synthesis of a pure form from readily available starting materials. Since tertiary aliphatic acetylenes do
not form readily under these conditions, the excess of alkyllithium
used is not particularly critical. The small amount of by-products that also form is similarly readily removed at the distillation stage.
1. Department of Chemistry and Applied Chemistry, University of Salford, Salford M5 4WT, England.
2. (a) A. J. Quillinan, E. A. Khan, and F. Scheinmann, Chem. Commun., 1030 (1974); (b) J. Klein and S. Brenner, J. Org. Chem., 36, 1319 (1971); (c) J. Klein and J. Y. Becker, Tetrahedron, 28, 5385 (1972); (d) J. Klein and J. Y. Becker, J. Chem. Soc., Perkin Trans. II, 599 (1973).
3. L. Clarke and E. R. Riegel, J. Amer. Chem. Soc., 34, 674 (1912).
4. R. M. Roberts, J. C. Gilbert, L. B. Rodewald, and A. S. Wingrove, “An Introduction to Modern Experimental Organic Chemistry”, Holt, Rinehart and Winston, New York, N. Y., 1969.
5. K. Hess and R. Bappert, Justus Liebigs Ann. Chem., 441, 151 (1925).
6. W. B. Renfrew, Jr., J. Amer. Chem. Soc., 66, 144 (1944).
7. T. L. Jacobs, Org. React. 5, 1 (1949).
8. V. Sawitsch, C. R. H. Seances Acad. Sci., 52, 399 (1861).
9. W. Morkownikoff, Bull Soc. Chim. Fr., 14, 90 (1861).
10. B. Gredy, Bull. Soc. Chim. Fr. [5], 2, 1951 (1935).
Chemical Abstracts Nomenclature (Collective Index Number; Registry
1-Hexyne, 3-ethyl- (8,9); ( —)
1-Hexyne (8,9); (693-02-7)
Lithium, butyl- (8,9); (109-72-8)
Ethyl bromide: Ethane, bromo- (8,9); (74-96-4)
Hexane, 3-cthyl- (8,9); (619-99-8)
1-Heptyne, 3-butyl- (8,9); ( —)
2-Heptanone, 3-butyl- (8,9); (997-69-3)
1. NaH, ethyl ether
B. 1
C. 2
Submitted by Lane A. Clizbe and Larry E. Overman1 Checked by A. Brossi, H. Mayer, and N. Kappeler
1. Procedure
Caution! Part A should be carried out in a well-ventilated hood to avoid exposure lo irichloroacetonitrile vapors.
A. Geraniol trichloroacetimidate (1). A dry 250-ml., threenecked flask is equipped with a magnetic stirring bar, a pressure-equalizing dropping funnel, a thermometer, and a nitrogen inlet tube. The apparatus is flushed with nitrogen and charged with 410 mg. (0.010 mole) of sodium hydride dispersed in mineral oil (Note 1) and with 15 ml. of hexane. The suspension is stirred, and the hydride is allowed to settle. The hexane is removed with a long dropping pipette, and 60 ml. of anhydrous ethyl ether is added. A solution of 15.4 g. (0.10 mole) of geraniol and 15 ml. of anhydrous ethyl ether is added over 5 minutes. After the evolution of hydrogen ceases (less than 5 minutes), the reaction mixture is stirred for an additional 15 minutes. The clear solution is then cooled to between —10 and 0° in an ice-salt bath. Trichloro-acetonitrile (10.0 ml., 14.4 g., 0.10 mole) is added dropwise to the stirred solution, while the reaction temperature is maintained below 0° (Note 2). Addition is completed within 15 minutes, and the reaction mixture is allowed to warm to room temperature. The light amber reaction mixture is poured into a 250-ml., round-bottomed flask, and the ethyl ether is removed with a rotary evaporator. Pentane [150 ml., containing 0.4 ml. (0.010 mole) of
methanol] is added, the mixture is shaken vigorously for 1 minute, and a small amount of dark, insoluble material is removed by gravity filtration. The residue is washed two times with pentane (50 ml. total), and the combined filtrate is concentrated with a rotary evaporator to afford 27-29 g. (90-97%) of nearly pure (Note 3) imidate 1.
B. 3,7-Dimethyl-3-trichloroacetamido-l,6-octadiene (2). A 500-ml., round-bottomed flask is equipped with a condenser, a magnetic stirring bar, and a calcium chloride drying tube. The flask is charged with the imidate 1 and 300 ml. of xylene. The solution is refluxed for 8 hours (Note 4). After cooling to room temperature the dark xylene solution is filtered through a short column (4.5 cm. in diameter) packed with silica gel (70 g.) and toluene. The column is eluted with an additional 250 ml. of toluene, and the combined light yellow eluant is concentrated with a rotary evaporator. Vacuum distillation through a 15-cm. Vigreux column yields 20-22 g. (67-74% for the two steps) of the octadiene 2 as a colorless liquid, b.p. 94—97° (0.03 mm.) (Note 5).
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