100 ml (201 mmol) of an aqueous 2M potassium carbonate solution and 4.4 g (3.80 mmol) of tetrakis palladium are introduced into a solution containing 33 g (77.3 mmol) of methyl (R)-2-tert-butoxycarbonylamino-3-(4-trifluoromethanesulfonyloxyphenyl)propionate, and 15 g (100 mmol) of 3-boronic acid-benzaldehyde (Example 28b) in 300 ml of ethylene glycol dimethyl ether. The reaction medium is heated at 85° C. for 20 h and, after a return to ambient temperature, extracted with ethyl acetate. The organic phase is washed with water and then a saturated sodium chloride solution, dried over magnesium sulfate, and concentrated. The residue obtained is purified by chromatography on a column of silica and eluted with a 7/3 heptane/ethyl acetate mixture. 10.2 g of coupled product are obtained with a 35% yield.
