Reacción #64781

Ecuación de reacción

bis(trimethylsilyl)trifluoroacetamide

ethyl acetate

2-trifluoromethyl-3-acetylthiopropionyl chloride

bis(trimethylsilyl)trifluoroacetamide

L-leucine

→

N-[2-[(Acetylthio)methyl]-3,3,3-trifluoro-1-oxopropyl]-L-leucine

Disolventes

methanol

acetic acid

hexane

acetonitrile

acetonitrile

Condiciones de reacción

Tratamiento posterior

1. 1
   Temperaturawas cooled to 0°-5° C.
2. 2
   Otroresulted in a clear lemon color solution
3. 3
   workup.STIRRINGon additional stirring for one hour at room temperature
4. 4
   TemperaturaThe reaction mixture was cooled to 0°-5° C.
5. 5
   workup.ADDITIONwas added dropwise over 45 minutes
6. 6
   workup.STIRRINGAfter stirring for 1.5 hours at 0°-5° C. to room temperature
7. 7
   Otrocompletion of the reaction
8. 8
   OtroThe reaction mixture was evaporated under reduced pressure
9. 9
   Otroto give a yellow oily residue which
10. 10
    Otrowas partitioned between ethyl acetate (75 mL) and water (50 mL)
11. 11
    ExtracciónThe aqueous phase was further extracted with ethyl acetate (4×50 mL)
12. 12
    Lavadothe combined extracts were washed with 75 mL of brine
13. 13
    Secadodried (MgSO4)
14. 14
    Otroevaporated
15. 15
    Otroto give 10.3 g
16. 16
    Otrochromatographed on 75 g
17. 17
    Otroof silica gel eluting with ethyl acetate: hexanes:acetic acid, 100:100:1 to yield 0.15 g
18. 18
    Lavadoof the faster eluting diastereomer (isomer A) and 0.12 g
19. 19
    Lavadoof slower eluting diastereomer (isomer B)
20. 20
    Otrochromatographed similarly (silica gel, 1300 g.) which
21. 21
    Otrogave 2.5 g
22. 22
    workup.ADDITIONof a mixture of both the diastereomers, and 1.5 g
23. 23
    OtroThe mixed fractions were rechromatographed
24. 24
    Otroto give 0.5 g
25. 25
    Otrotriturated with hexanes containing a few drops of ethyl acetate
26. 26
    Filtraciónfiltered
27. 27
    Otrodried
28. 28
    Otroto yield 2.57 g

Procedimiento

A stirred suspension of L-leucine (2.62 g., 20 mmol) in 35 mL of dry acetonitrile under argon was cooled to 0°-5° C. and bis(trimethylsilyl)trifluoroacetamide (10.62 mL, 40 mmol) was added. The reaction mixture was allowed to stir while slowly warming to room temperature. After 2 hours, another 3.5 mL (13 mmol) of bis(trimethylsilyl)trifluoroacetamide was added which resulted in a clear lemon color solution on additional stirring for one hour at room temperature. The reaction mixture was cooled to 0°-5° C. and 2-trifluoromethyl-3-acetylthiopropionyl chloride (4.69 g., 20 mmol.) dissolved in 8 mL of acetonitrile was added dropwise over 45 minutes. After stirring for 1.5 hours at 0°-5° C. to room temperature, TLC shows completion of the reaction. The reaction mixture was evaporated under reduced pressure to give a yellow oily residue which was partitioned between ethyl acetate (75 mL) and water (50 mL). The aqueous phase was further extracted with ethyl acetate (4×50 mL), the combined extracts were washed with 75 mL of brine, dried (MgSO4), and evaporated to give 10.3 g. of a yellow semi-solid residue. A 0.68 g. portion of this crude material was flash chromatographed on 75 g. of silica gel eluting with ethyl acetate: hexanes:acetic acid, 100:100:1 to yield 0.15 g. of the faster eluting diastereomer (isomer A) and 0.12 g. of slower eluting diastereomer (isomer B). The remaining 9.6 g. of crude material was flash chromatographed similarly (silica gel, 1300 g.) which gave 2.5 g. of isomer A, 2.7 g. of a mixture of both the diastereomers, and 1.5 g. of isomer B. The mixed fractions were rechromatographed using the same conditions to give 0.5 g. of isomer A and 1.25 g. of isomer B. Both the 2.5 g. and 0.5 g. portions of isomer A were combined, triturated with hexanes containing a few drops of ethyl acetate, filtered, and dried to yield 2.57 g. of the title isomer A product as a white crystalline solid, m.p. 150°-152° C., TLC Rf =0.40 (100:50:1 ethyl acetate:hexane:acetic acid), [α]D =-146.9° (c=1.00, methanol).

Fuente