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For acyl halides or anhydrides which do not afford ketenes in the presence of base (such as perfluoroacyl halides), however, the a-acylmethylenephosphoranes can be prepared directly in one step from the phosphonium salts by using two equivalents of base by the present procedure (Table I).2 Both tetrahydrofuran and methylene chloride have been used as solvents and in the case of the title compound, tetrahydrofuran provides the best results. Good yields of the phosphoranes are generally obtained when R1 is an electron-withdrawing group such as ester or nitrile. The yields of phosphoranes obtained for the thiomethyl or phenyl cases can be
improved by using 1,4-diazabicyclo[2.2.2]octane (DABCO) rather than triethylamine as the base.
1. Monsanto Agricultural Company, A Unit of Monsanto Company, 800 N. Lindbergh Blvd., St. Louis, MO 63167.
2. Hamper, B. C. J. Org. Chem. 1988, 53, 5558.
3. Huang, Y.; Shen, Y.; Xin, Y.; Wang, Q.; Wu, W. Sei. Sin. (Engl. Ed.) 1982, 25, 21.
4. For some recent examples, see Shen, Y.; Zheng, J.; Huang, Y. J. Fluorine Chem. 1988, 41, 363; Braga, A. L.; Comasseto, J. V.; Petragnani, N. Tetrahedron Lett. 1984, 25, 1111; Kobayashi, Y.; Yamashita, T.; Takahashi, K.; Kuroda, H.; Kumadaki, I. Chem. Pharm. Bull. 1984, 32, 4402; Shen, Y.; Lin, Y.; Xin, Y. Tetrahedron Lett. 1985, 26, 5137.
5. Braga, A. L.; Comasseto, J. V.; Petragnani, N. Synthesis 1984, 240.
6. Froissard, J.; Greiner, J.; Pastor, R.; Cambon, A. J. Fluorine Chem. 1981, 17, 249; Chauvin, A.; Greiner, J.; Pastor, R.; Cambon, A. J. Fluorine Chem. 1984,
7. Poulter, C. D.; Wiggins, P. L.; Plummer, T. L. J. Org. Chem. 1981, 46,1532.
8. Hirao, K.; Yamashita, A.; Yonemitsu, O. J. Fluorine Chem. 1987, 36, 293.
9. Yamanaka, H.; Araki, T.; Kuwabara, M.; Fukunishi, K.; Nomura, M. Nippon Kagaku Kaishi, 1986, 1321; Chem. Abstr. 1987, 107, 175447f.
10. Bestmann, H. J. Chem. Ber. 1962, 95, 58.
11. Lang, R. W.; Hansen, H.-J. Helv. Chim. ActalQSO. 63, 438; Lang, R. W.; Hansen, H.-J. Org. Synth., Coll. Vol. VI11990, 232.
PREPARATION OF (a-ACYLMETHYLENE)PHOSPHORANES FROM a-SUBSTITUTED METHYLPHOSPHONIUM SALTS2
geq'Dase , Ph3P=<
R1 R2 Solvent Base Yield (%)
C02Et CF3 CH2CI2 Et3N 54
C02Me CF3 THF Et3N 99
C02Et CF2CF3 THF Et3N 69
CN CF3 THF Et3N 75
SCH3 CF3 THF Et3N 49
Ph CF3 CH2CI2 Et3N 24
Ph CF3 CH2CI2 DABCO 57
Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)
Ethyl 4,4,4-trifluorotetrolate: 2-Butynoic acid, 4,4,4-tritluoro-, ethyl ester (10); (79424-03-6)
Ethyl 4,4,4-trifluoro-2-(triphenylphosphoranylidene)acetoacetate: Butanoic acid, 4,4,4-trifluoro-3-oxo-2-(triphenylphosphoranylidene)-, ethyl ester (11); (83961-56-2) (Carbethoxymethyl)triphenylphosphonium bromide; Phosphonium, (carboxymethyi)triphenyl-, bromide, ethyl ester (8); Phosphonium, (2-ethoxy-2-oxoethyl)triphenyl-, bromide (9); (1530-45-6)
Trifluoroacetic anhydride: Acetic acid, trifluoro-, anhydride (8,9); (407-25-0) Triphenylphosphine: Phosphine, triphenyl- (8,9); (603-35-0)
Ethyl bromoacetate: Acetic acid, bromo-, ethyl ester (8,9); (105-36-2)
SYNTHESIS OF 0-KETO ESTERS BY C-ACYLATION OF PREFORMED ENOLATES WITH METHYL CYANOFORMATE: PREPARATION OF METHYL (1a,4ap,8aa)-2-OXODECAHYDRO-1-NAPHTHOATE
Li, NH3 (liq.)
Submitted by Simon R. Crabtree, Lewis N. Mander, and S. Paul Sethi.1 Checked by Thierry Vandenheste and Leo A. Paquette.
Caution! Cyanide salts are formed in this procedure. All procedures should be conducted in a well-ventilated hood and rubber gloves should be worn.
Liquid ammonia (350 mL) is dried over sodium amide for 20 min (Note 1), then distilled under a positive pressure of dry nitrogen into a flame-dried, 1-L, three-necked, round-bottomed flask equipped with a dry ice condenser, rubber septum and magnetic stirring bar. The flask is cooled to -78°C and small pieces of lithium (1.11 g, 0.16 mol) (Note 2) are added over 10 min to afford a deep blue solution. A solution of enone 1 (10.08 g, 0.07 mol) (Note 3) in tert-butyl alcohol (5.10 g, 0.07 mol) (Note 4) and ether (40 mL) (Note 5) is added dropwise over a 15-min period at -78°C, and then sufficient isoprene (Note 6) is added dropwise to discharge the residual blue color of the reaction mixture. The ammonia is allowed to evaporate under a stream of dry nitrogen and the ether is removed under reduced pressure to leave a white foam. After a further 5 min under high vacuum, the nitrogen atmosphere is restored, the lithium
enolate 2 is suspended in dry ether (80 mL) at -78°C by vigorous stirring, and methyl cyanoformate (6.73 g, 0.08 mol) (Note 7) is added over a 5-min period. Stirring is maintained at this temperature for a further 40 min and then the mixture is allowed to warm to 0°C. Water (500 mL) and ether (200 mL) are added and the mixture is stirred vigorously until the precipitate has dissolved. After separation of the organic layer, the aqueous phase is extracted with ether (2 x 300 mL), the combined extracts are washed with water (200 mL) and brine (200 mL) (Note 8), and then dried over anhydrous magnesium sulfate. Removal of solvent under reduced pressure furnishes a pale yellow oil which is dissolved in hexane (200 mL); the solution is kept in the freezer (-28°C) for approximately 1.5 hr, after which time very pale yellow crystals of the p-keto ester 3 are deposited. These are collected by filtration at low temperature and after concentration of the mother liquors, two further crops are collected. Flash chromatography (ethyl acetate/hexane, 13:87) on silica gel (140 g) (Note 9) of the residue (3.5 g) from the remaining mother liquor followed by two recrystallizations affords further 3. The total quantity of 3 obtained is 11.5-11.8 g (81-84% yield) (Note 10).