Reaction #1552074

Reaction equation

NaOH

Crotonaldehyde

BF3.OEt2

5-methyl-3-methylenehex-1-ene

→

3b

Yield 94.0%

4-Isobutyl-6-methylcyclohex-3-enecarbaldehyde

Yield 94.0%

Solvents

methylene chloride

methylene chloride

Conditions

Workup

1. 1
   Temperatureto warm to −20° C
2. 2
   workup.STIRRINGThe solution was stirred at this temperature for a further 1.5 h
3. 3
   OtherAfter brief agitation the phases were separated
4. 4
   Washthe lower organic phase washed with water (100 ml) and brine (2×100 ml)
5. 5
   ExtractionThe combined aqueous phases were extracted with MTBE (150 ml), phase
6. 6
   Otherseparated
7. 7
   Washthe upper organic part washed to neutral with brine
8. 8
   Dryingdried (Na2SO4)
9. 9
   Concentrationconcentrated in vacuo

Procedure

Crotonaldehyde cis/trans (16 g, 230 mmol) was dissolved in methylene chloride and cooled to −30° C. With stirring, and under nitrogen, BF3.OEt2 (3.6 ml, 29 mmol) was added gradually. A solution of 5-methyl-3-methylenehex-1-ene 2 (21 g, 191 mmol) in methylene chloride (50 ml) was then added at −30° C. over 1 h and the pot allowed to warm to −20° C. The solution was stirred at this temperature for a further 1.5 h before being poured onto 2M NaOH (100 ml). After brief agitation the phases were separated and the lower organic phase washed with water (100 ml) and brine (2×100 ml). The combined aqueous phases were extracted with MTBE (150 ml), phase separated and the upper organic part washed to neutral with brine. The organic phases were combined, dried (Na2SO4) and concentrated in vacuo to afford 3b as a pale yellow oil (33 g, 94% yield; 98% pure). The product was used in the next steps without further purification.

Source