To stirred solution of 9.1 g (45 mmol) 1b, 15.8 g (45 mmol) 5a and one drop of glacial acid in 60 ml dichloroethane (pH=5) were added 14.8 g (70 mmol) sodium tris-acetoxy hydro borane. The reaction mixture was stirred over night and diluted with 5 ml water. The pH value was adjusted with aqueous sodium hydroxyd solution to pH=8-9. The mixture was extracted three times with dichloromethane. The combined organic phases were washed with water and brine and were dried with magnesium sulfate. The desired crude product 5b was obtained in 71% yield (17.2 g, 32.0 mmol) as yellow oil. The crude product 5b was used without further purification.
