The reaction product obtained by conducting the Michael-addition reaction in the same manner as in Example 116 using 5.7 ml of a 1.5M cyclohexane solution of lithium diisopropylamide, 2.6 g of trityl acetate and 3.2 g of dibenzhydryl maleate, was dissolved in a liquid mixture of 20 ml of acetic acid and 5 ml of water, and the solution was left to stand at room temperature overnight and then evaporated to dryness under reduced pressure. The residue was subjected to silica gel column chromatography (chloroform/methanol=100/1→10/1) to obtain 1.05 g (yield: 29%) of the above-identified compound as white crystalline powder having a melting point of from 105° to 106° C.
