12.6g of intermediate (A) and 500 mL of tetrahydrofuran (dehydrated) were put in a flask, and the resultant
was cooled to -78??C. 28 mL of n-BuLi (1.60M in hexane) was added, and stirring was conducted for 2 hours while
elevating the temperature to 0??C. Then, the solution was again cooled to -78??C, and 11.6g of B(OMe) 3 was added. After
stirring at 10 minutes at -78??C, stirring was further conducted for 5 hours while gradually elevating the temperature to
room temperature. After completion of the reaction, 1 N HCl aq. (100 mL) was added, and the reaction solution was stirred at room
temperature for 1 hour. Then, the solution was transferred to a separating funnel, and extracted with ethyl acetate. This solution was dried with MgSO 4, concentrated and washed with hexane, whereby 7.2g (yield: 65%) of white
solids of intermediate (B) were obtained.