Reaction #2146737

Reaction equation

K2CO3

1,3-Pentadiene

BF3.OEt2

3-hexen-2-one

→

1-(rel-(1R,2S,6S)-6-ethyl-2-methylcyclohex-3-enyl)ethan-1-one

Solvents

dichloromethane

Conditions

Workup

1. 1
   Temperature1 h at 20° C. before being cooled at 0° C.
2. 2
   workup.STIRRINGThe resulting mixture was stirred 40 min.
3. 3
   Concentrationconcentrated (43° C. till 300 mbar)
4. 4
   WashThe aqueous phase was washed with hexane (500 ml)
5. 5
   Dryingthe combined organic phases with 20% aqueous K2CO3 (100 ml), three times with saturated aqueous NaCl solution, dried (MgSO4)
6. 6
   Concentrationconcentrated
7. 7
   workup.DISTILLATIONSulzer-distillation (0.4-0.1 mbar) of the crude product (400 g)

Procedure

At −15° C., a solution of BF3.OEt2 (54 g, 0.38 mol) in dichloromethane (680 ml) was treated within 10 min. with 3-hexen-2-one (220.1 g, 89% pure, 2 mol). 1,3-Pentadiene (490 g, 7.2 mol, precooled at 0° C.) was then added and the resulting solution stirred 30 min. at 0° C. then 1 h at 20° C. before being cooled at 0° C. and treated with a solution of 20% aqueous K2CO3 (250 ml). The resulting mixture was stirred 40 min. and concentrated (43° C. till 300 mbar). The aqueous phase was washed with hexane (500 ml) and the combined organic phases with 20% aqueous K2CO3 (100 ml), three times with saturated aqueous NaCl solution, dried (MgSO4) and concentrated. Sulzer-distillation (0.4-0.1 mbar) of the crude product (400 g) gave 1-(rel-(1R,2S,6S)-6-ethyl-2-methylcyclohex-3-enyl)ethan-1-one (326 g, 98% yield).

Source