Hydroquinone → 6-hydroxy-4,4-dimethyl-3,4-dihydro-2H-1-benzopyran-2-one

A mixture of 8.8 g of hydroquinone, 5 g of methyl 3,3-dimethylacrylate and 0.4 g of conc. sulfuric acid was heated at 130° C. for 4 hours. The reaction mixture was cooled, and then 15 ml of toluene was added. The crystals that precipitated were separated by filtration. The filtrate was concentrated and then distilled under reduced pressure to give 4.6 g (yield 70%) of 3,4-dihydro-4,4-dimethyl-6-hydroxycoumarin as pale pink crystals (melting point 95°-96° C.). The crystals (3.0 g) were dissolved in 10 ml of tetrahydrofuran, and the solution was added dropwise at room temperature to a mixture of 0.9 g of lithium aluminum hydride and 20 ml of tetrahydrofuran. The mixture was then refluxed for 4 hours. The reaction mixture was worked up in a customary manner, and the crude product, without purification, was dissolved in 30 ml of toluene. A catalytic amount of p-toluenesulfonic acid was added to the solution, and the mixture was heated at 120° C. for 1.5 hours. In a customary manner, the reaction mixture was worked up, and the residue after concentration was isolated and purified by column chromatography to give 2.4 g (yield 85%) of the desired product as a yellow orange liquid.