The general procedure for the synthesis of 6,7-dichlorochroman-4-one from 3-(3,4-dichlorophenoxy)propionic acid is as follows:
1. 500 mg of 3-(3,4-dichlorophenoxy)propionic acid was suspended in 50 mL of liquid hydrogen fluoride and the reaction system was cooled in a solid carbon dioxide/acetone bath.
2. The reaction mixture was stirred overnight, during which time the cooling bath was not replenished.
3. Upon completion of the reaction, the hydrogen fluoride is removed by a stream of air.
4. The residual solid is dissolved in ether and washed with 10% aqueous sodium carbonate.
5. The organic layer is separated and dried over anhydrous magnesium sulfate, followed by evaporation of the solvent to give 6,7-dichloro-2,3-dihydro-4-one (PCI 65C) of sufficient purity.
Product Characterization:
PCI 65C was an off-white solid, yield: 350 mg (76%).
1H NMR (CDCl3, 400 MHz) δ: 2.79 (t, 2H), 4.52 (t, 2H), 7.10 (s, 1H), 7.90 (s, 1H).
13C NMR (CDCl3, 100 MHz) δ: 37.4, 67.6, 118.0, 120.2, 120.9, 126.0, 128.3, 140.0, 160.3, 189.9.
