p-Toluenesulfonic acid → 6-Bromo-2,2,3-trimethyl-2H-benzo[b]pyran

HRID 1420753Notes

Reaction equation

HRID 1420753 reaction equation
[Br:1][C:2]1[CH:15]=[CH:14][C:5]2[O:6][C:7]([CH3:13])([CH3:12])[CH:8]([CH3:11])[C:9](=O)[C:4]=2[CH:3]=1.[BH4-].[Na+].C1(C)C=CC(S(O)(=O)=O)=CC=1>C(O)C.C1(C)C=CC=CC=1>[Br:1][C:2]1[CH:15]=[CH:14][C:5]2[O:6][C:7]([CH3:12])([CH3:13])[C:8]([CH3:11])=[CH:9][C:4]=2[CH:3]=1

Participants

6

Reactant 3

HCID 6101p-Toluenesulfonic acidHCID 4311764Sodium borohydrideHCID 157815536-bromo-3,4-dihydro-4-oxo-2,2,3-trimethyl-2H-benzo[b]pyran

Product 1

HCID 149560896-Bromo-2,2,3-trimethyl-2H-benzo[b]pyranYield 91.4%

Reagents, catalysts & solvents 2

HCID 702EthanolSolventHCID 1140TolueneSolvent

Procedure

6-Bromo-3,4-dihydro-4-oxo-2,2,3-trimethyl-2H-benzo[b]pyran (407 g) (see Preparation 3) was dissolved in ethanol (1500 ml), cooled in an ice bath and sodium borohydride (61.4 g) was added portionwise over 20 minutes. The mixture was stirred at room temperature for 3 hours, the solvent removed under reduced pressure, the residue dissolved in diethyl ether and the mixture washed first with water and then with brine. The organic layer was dried (anhydrous magnesium sulphate) and the solvent removed to yield the crude alcohol. This was dissolved in toluene (1000 ml), para-toluenesulphonic acid (40 g) added and the mixture heated under reflux (with removal of water) for 2 hours. The solvent volume was reduced to approximately 500 ml and the solution was washed with aqueous sodium carbonate solution and then brine. The organic phase was dried (anhydrous magnesium sulphate) and the solvent removed under reduced pressure to yield 6-bromo-2,2,3-trimethyl-2H-benzo[b]pyran (350 g) as an orange oil.

Workup

  1. temperaturecooled in an ice bath
  2. customthe solvent removed under reduced pressure
  3. dissolutionthe residue dissolved in diethyl ether
  4. washthe mixture washed first with water
  5. dry with materialThe organic layer was dried (anhydrous magnesium sulphate)
  6. customthe solvent removed
  7. customto yield the crude alcohol
  8. temperaturethe mixture heated
  9. temperatureunder reflux
  10. custom(with removal of water) for 2 hours
  11. washthe solution was washed with aqueous sodium carbonate solution
  12. dry with materialThe organic phase was dried (anhydrous magnesium sulphate)
  13. customthe solvent removed under reduced pressure

Sources & evidence

ORD record
ord-7fe28e5af7b84821b26237adf7282be3
Source dataset
uspto-grants-2000_06
Patent number
US06071938

Reaction notes

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