反应详情

(1-Methyl-(E)-2-butenyl)triphenylphosphonium bromide from Example 9 (0.62 g, 0.0015 mole) was added to a dry flask with 5 ml tetrahydrofuran. The flask was equipped with magnetic stirrer and septum; the reaction was carried out under nitrogen. The salt did not dissolve completely but became a sticky suspension. The mixture was cooled over ice, and butyllithium (2.5M in hexane) was added dropwise, with stirring, until the color change became permanent; then an additional 0.0015 mole was added. The solid in the flask dissolved as it was converted to the ylide. One hundred milligrams of 2,4-dimethyl-(E,E)-2,4-hexadienal (0.0008 mole), compound 4, R1 =H, prepared previously by Pattel and Pattenden (1985), was added to the Wittig reagent, and the mixture was allowed to warm to room temperature. The mixture was stirred for 2 hr, and it was again cooled over ice. Water was added dropwise until the red color of the solution had disappeared, and ca. 2 ml more water was added. The mixture was diluted with hexane and the organic layer dried over sodium sulfate. The solvent was removed and the product passed through a silica column with hexane. By capillary GC the product was 61% the (E,E,E,E) isomer, ca. 31% the (E,E,Z,E) isomer, and ca. 8% by-products, after clean-up on silica. Further purification on the AgNO3HPLC column yielded the (E,E,E,E) isomer in >97% purity.

1. customThe flask was equipped with magnetic stirrer
2. dissolutionThe salt did not dissolve completely
3. additionwas added dropwise
4. additionthen an additional 0.0015 mole was added
5. dissolutionThe solid in the flask dissolved as it
6. stirringThe mixture was stirred for 2 hr
7. temperatureit was again cooled over ice
8. dry with materialthe organic layer dried over sodium sulfate
9. customThe solvent was removed
10. customFurther purification on the AgNO3HPLC column
11. customyielded the (E,E,E,E) isomer in >97% purity