Reaktion #55052

Reaktionsgleichung

boron trifluoride etherate

isobutylene

phosphoric acid

NaHCO3

CH2Cl2

dry ice acetone

CH2Cl2

→

desired product

(S)-(+)tert. Butyl 3-tert. butoxy-2-methylpropionate

Lösungsmittel

water

Reaktionsbedingungen

Aufarbeitung

1. 1
   workup.ADDITIONTo the resulting mixture was added
2. 2
   workup.STIRRINGThe resulting mixture was stirred at -72° C. for 2 hours and at 0-5° C. (ice bath) for 20 hours
3. 3
   workup.ADDITIONthen treated with 300 g
4. 4
   SonstigeThe CH2Cl2 layer was removed
5. 5
   Extraktionthe aqueous layer was extracted twice with CH 2 Cl2
6. 6
   WaschenThe combined organic extracts were washed twice with brine
7. 7
   Trocknenthen dried (MgSO4)
8. 8
   Filtrationfiltered
9. 9
   Einengenconcentrated in vacuo
10. 10
    Sonstigegiving 23.3 g
11. 11
    SonstigeThis material was chromatographed on 200 g
12. 12
    WaschenElution with 19:1 parts by volume and 9:1 parts by volume hexane-ether

Vorschrift

A solution of 8.7 g. of S-(+)-β-hydroxyisobutyric acid in 140 ml. of CH2Cl2 was stirred and cooled to -72° C. (dry ice-acetone bath) whereupon 70 ml. of liquid isobutylene was added rapidly. To the resulting mixture was added with stirring at -72° C., a solution of 1.6 ml. of phosphoric acid (prepared by dissolving 5 g. of phosphorus pentoxide in 11 ml. of 85% by weight phosphoric acid) in 10 ml. of CH2Cl2, dropwise followed by 3.5 ml. of boron trifluoride etherate also dropwise. The resulting mixture was stirred at -72° C. for 2 hours and at 0-5° C. (ice bath) for 20 hours then treated with 300 g. of ice-water followed by a solution of 19 g. of NaHCO3 in 200 ml. of water. The CH2Cl2 layer was removed and the aqueous layer was extracted twice with CH 2 Cl2. The combined organic extracts were washed twice with brine then dried (MgSO4), filtered and concentrated in vacuo giving 23.3 g. of crude product as a yellow oil. This material was chromatographed on 200 g. of silica gel. Elution with 19:1 parts by volume and 9:1 parts by volume hexane-ether gave the desired product which was distilled yielding 12.7 g. (79%) of the ether ester (S)-(+)-tert. butyl 3-tert. butoxy-2-methylpropionate as a colorless liquid, b.p. 99° C. (22 mm Hg.); [α]25D+ 19.52° (c 4.25, CH3OH).

Quelle