160 mg of 7-allyl-6-methoxy-1-methyl-1,4-dihydrobenz[d][1,3]oxazin-2-one was dissolved in 20 ml of t-butanol-water (1:1). Thereafter, 0.96 g of AD-mix-β was added to the reaction solution, and the obtained mixture was then stirred at room temperature overnight. Thereafter, 1.03 g of sodium sulfite was added to the reaction solution while cooling on ice, and the obtained mixture was stirred at room temperature for 1 hour. A saturated sodium chloride aqueous solution was added to the reaction solution, followed by extraction with methylene chloride. The extract was dried over magnesium sulfate and then concentrated under a reduced pressure, so as to obtain 280 mg of 7-(2,3-dihydroxypropyl)-6-methoxy-1-methyl-1,4-dihydrobenz[d][1,3]oxazin-2-one. This compound was used in the following reaction without further purification.
