To a mixture of 300 mg of the mixture from step 3 and 360 mg 4-formylphenylboronic acid in 9 ml 1,2-dimethoxyethane are added 1.8 ml of a 10% w/w sodium carbonate solution and 36 mg dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium (II) and the resulting mixture is heated to 80° C. under an inert gas atmosphere for 18 h. The work up is performed by diluting the reaction mixture with water and dichloromethane, separating the phases and extraction of the aqueous phase with dichloromethane. The combined organic layers are dried over sodium sulphate, evaporated and the residue is purified by chromatography on silica gel (dichloromethane/methanol). The product is crystallized from ethyl acetate.
