[step 1] Lithium diisopropylamide (2.0 mol/L heptane/THF/ethylbenzene solution, 100 mL, 200 mmol) was diluted with THF (40 mL), a solution of propiononitrile (7.13 mL, 100 mmol) in THF (40 mL) was added dropwise while stirring at 0° C. over 15 min. After stirring at 0° C. for 30 min, a solution of diethyl chlorophosphate (14.4 mL, 100 mmol) in THF (40 mL) was added dropwise over 45 min. After stirring at room temperature for 2 hr, methyl 11-oxo-6,11-dihydrodibenzo[b,e]oxepine-3-carboxylate (JP-B-2526005, 10.7 g, 40 mmol) was added, and the mixture was stirred at room temperature for 1.5 hr. To the mixture were added ethyl acetate and water, and the mixture was extracted with 3 times with ethyl acetate. The organic layer was washed with brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate:hexane=15:85) to give (Z)-11-(1-cyanoethylidene)-6,11-dihydrodibenzo[b,e]oxepine-3-carboxylic acid methyl ester (4.47 g, 14.6 mmol, 37%) and (E)-11-(1-cyanoethylidene)-6,11-dihydrodibenzo[b,e]oxepine-3-carboxylic acid methyl ester (6.40 g, 21.0 mmol, 53%).
