2-methyl-2,3-dihydrochromen-4-one

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 2,3-dihydro-2-methyl-4H-1-benzopyran-4-one (1.62 g) is dissolved in ethanol 95% (50 ml) and the solution is refluxed under stirring. In 10-15 minutes isoamylnitrite (8 ml) and concentrated HCl (40 ml) are added drop by drop. Heating and stirring are stopped, and the resulting mixture is allowed to stand ca. 2 hours. Then water (200 ml) is added until precipitation of a white solid. The solvent is evaporated, obtaining a solid product which is dissolved in a little volume of chloroform and purified on silica gel in equilibrium with the same solvent. The purified product contains a low percentage of yellow impurities which can be completely eliminated by crystallisation in acetone. The residual solvent is then eliminated, obtaining 0.97 g of 3-hydroxy-2-methyl-4H-1-benzopyran-4-one (colourless crystals; m.p.=179-180° C.; IR: 1632, 1666 e 3301 cm−1; yield=51%). the solution is refluxed Heating stirring The solvent is evaporated obtaining a solid product which purified on silica gel in equilibrium with the same solvent can be completely eliminated by crystallisation in acetone