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

참여 물질

반응 단계

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), paratoluenesulphonic 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.

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