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Organic Synteses vol 70 - Meyers A.I.

Meyers A.I. , Boecman R.K. Organic Synteses vol 70 - John Wiley & Sons, 1992. - 163 p.
ISBN 0-471-57743
Download (direct link): organicsynthesesvol701992.pdf
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V
2. NCC02Me, Et20 (62% yield)
+
4
C02Me 5 (75% ds)
C02Me 6 (25% ds)
260
o
‘OMe
1. U, NH3, (CH3)3COH
2. NCC02Me, Et20 (71% yield)
o
CC^Me
8 (>98% ds)
‘OMe
7
For compounds in which the p-carbon of the enolate is stericaliy hindered, this problem can normally be eliminated by the use of diethyl ether as the solvent. In several cases a switch from exclusive O-acylation in tetrahydrofuran to complete C-acylation in ether has been observed, and the conversion of 7 into 8 provides a typical illustration. When 3-methyl-2-cyclohexen-1-one 9 is converted into 10 by the addition of lithium dimethyl cuprate followed by in situ reaction with methyl cyanoformate, however, enol carbonate 11 accounts for 6% of the products. This can be avoided if the intermediate enolate is trapped as the enol trimethylsilyl ether and the enolate reliberated by treatment with butyllithium (note that the traditional reagent, methyllithium, is ineffective in ether as a solvent), but the overall yield is reduced.
Quite apart from the issue of regioselectivity, the present method is exceptionally reliable and makes it possible to prepare p-keto esters from ketones under especially mild conditions. It is not only the method of choice with sensitive substrates, but will often ensure superior results with more stable intermediates as well.8.16 A wide range of examples is provided in the Table, while further examples have been reported elsewhere.17 The methodology has also been applied to
COzMe
10 (78% yield)
11 (6% yield)
261
esters,12 lactones,18 and the N-acylation of lactams.19 The formation of ß-diketones
by the treatment of lithium enolates with alkanoyl and aroyl nitriles has also been
described.20
1. Research School of Chemistry, Australian National University, G.P.O. Box 4, Canberra, A.C.T., 2601, Australia.
2. Childs, M. E.; Weber, W. P. J. Org. Chem. 1976, 41, 3486.
3. Mander, L. N.; Sethi, S. P. Tetrahedron Lett. 1983, 24, 5425.
4. Caine, D. In "Carbon-Carbon Bond Formation"; Augustine, R. L., Ed.; Marcel Dekker: 1979; Vol. 1, pp 250-258.
5. Seebach, D.; Weller, T.; Protschuk, G.; Beck, A. K.; Hoekstra, M. S. Helv. Chim. Acta 1981, 64, 716.
6. Caine, D. Org. React. 1976, 23, 1-258.
7. Caine, D. In "Carbon-Carbon Bond Formation"; Augustine, R. L., Ed.; Marcel Dekker: 1979; Vol. 1, p 258, footnote 69.
8. Kende, A. S.; Becker, D. A. Synth. Commun. 1982, 12, 829.
9. Vedejs, E.; Nader, B. J. Org. Chem. 1982, 47, 3193.
10. Hellou, J.; Kingston, J. F.; Fallis, A. G. Synthesis 1984, 1014.
11. Ziegler, F. E.; Klein, S. I.; Pati, U. K.; Wang, T.-F. J. Am. Chem. Soc. 1985, 107, 2730.
12. (a) Winkler, J. D.; Henegar, K. E.; Williard, P. G. J. Am. Chem. Soc. 1987, 109, 2850; (b) Henegar, K. E.; Winkler, J. D. Tetrahedron Lett. 1987, 28, 1051.
13. Kunisch, F.; Hobert, K.; Welzel, P. Tetrahedron Lett. 1985, 26, 5433.
14. Crabtree, S. R.; Chu, W. L. A.; Mander, L. N. Synlett. 1990, 169
15. Evans, D. A. In "Asymmetric Synthesis"; Morrison, J. D., Ed.; Academic Press: Orlando, FL, 1984; Vol. 3, pp 1-110.
16. Mori, K.; Ikunaka, M. Tetrahedron, 1987, 43, 45.
262
17. (a) Miyata, O.; Hirata, Y.; Naito, T.; Ninomiya, I. Heterocycles 1984, 22, 1041; (b) Schuda, P. F.; Phillips, J. L; Morgan, T. M. J. Org. Chem. 1986, 51, 2742; (c) Haynes, R. K.; Katsifis, A. G. J. Chem. Soc., Chem. Commun. 1987, 340.
18. Ziegler, F. E.; Cain, W. T.; Kneisley, A.; Stirchak, E. P.; Wester, R. T. J. Am. Chem. Soc. 1988, 110, 5442.
19. (a) Melching, K. H.; Hiemstra, H.; Klaver, W. J.; Speckamp, W. N. Tetrahedron Lett. 1986, 27, 4799; (b) Esch, P. M.; Hiemstra, H.; Klaver, W. J.; Speckamp, W. N. Heterocycles, 1987, 26, 75.
20. Howard, A. S.; Meerholz, C. A.; Michael, J. P. Tetrahedron Lett. 1979, 1339.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)
Methyl cyanoformate: Formic acid, cyano-, methyl ester (8); Carbonocyanidic acid, methyl ester (9); (17640-15-2)
A1 (9)-Octalone-2: 2(3H)-Naphthalenone, 4,4a,5,6,7,8-hexahydro- (8,9); (1196-55-0) Isoprene (8); 1,3-Butadiene, 2-methyl- (9); (78-79-5)
263
TABLE
PREPARATION OF [l-KETO-ESTERS BY THE KINETICALLY CONTROLLED C-ACYLATION OF LITHIUM ENOLATES WITH METHYL CYANOFORMATE
Entry 1 Substrate CH3(CH2)n^|f' O 0 Procedure* A Product CH3(CH2)n/~Y~''C02Me 0 n= 1 o "“4 Yieid(%) 84 86
2 "-6 o A R ^A.COzMe XJ R=H R = Me 0 86 86
3 6 A 0 co,Me 6 96
4 A /fv° /A^£.C02Me 85
5 OSiM@3 A o R^A^C02Me R*Me OSiMe3 71 75
6 <y —(CH2)n B Og M© —{CH2)n n = i n = 2 72 68
7 o A 0 /^A^COgMe 65
8 0 6 A A 0 KC02Me u 0 84
9 ci) A c£f~ CO2M0 92
10 03° A <xf 92
11 Ctx C Cfe 85
COjMs
^Procedures: A: Reference 3: B: Lithium enolates generated by addition of
methyllithi""’ thf nt -78"C, C: As doscribod for the conversion of enone 1 into P-
OXIDATION OF SECONDARY AMINES TO NITRONES 6-METHYL-2,3,4,5-TETRAHYDROPYRIDINE N-OXIDE (Pyridine, 2,3,4,5-tetrahydro-6-methyl-, 1-oxide)
[^1 , Cl
N^CHa H20 CH3
H Or
Submitted by Shun-lchi Murahashi, Tatsuki Shiota, and Yasushi Imada.1 Checked by Gary C. Look and Larry E. Overman.
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