Acetic Acid → ethyl 3,4-dihydro-1H-2-benzopyran-1-acetate

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Reaction Steps

Ethyl 2-(2-hydroxyethyl)cinnamate (CXXX, EXAMPLE 112, theoretically 2.40 moles) is dissolved in THF (2.4 liters) and cooled to 0°. Potassium t-butoxide (5 mol %, 120 ml of a 1 molar THF solution) is added via syringe. After 5 min HPLC shows the cyclization is completed. Acetic acid (6 mol %, 8.2 ml, 144 mmol) is added. The slurry is filtered through approximately 300 g of 200 mesh silica gel. The solvent is removed under reduced pressure until approximately 0.5 liter of THF remained. Diatomaceous earth (100 g) is added followed by hexane (4.5 liters). This slurry is filtered through 200 mesh silica gel (400 g), washing with THF/hexane (1/9) until TLC shows no remaining product. Solvent removal gives the title compound. This material is filtered through silica gel more carefully, giving an analytical sample of the title compound, NMR (300 MHz, CDCl3) 7.1-7.2, 7.05, 5.26, 4.23, 4.12, 3.83, 3.0-2.7, 1.28; high resolution MS calculated for 220.1099, found 220.1105.

Provenance & Evidence