Process for the preparation of elafibranor and novel synthesis intermediates

A one-pot process comprising the following steps:

• a′. in an aprotic solvent comprising compound (II) or (IIa),
• wherein X is an alkali or an alkali-earth metal;
• R is —CHO or
• optionally in the presence of a protic co-solvent and in the presence of a strong base comprising sodium or potassium hydroxide thus obtaining a mixture;
• b′. optionally heating the mixture and adding (III)
• and, when R is —CHO adding 4′-(methylthio)acetophenone of formula (V)
• c′. acidifying the mixture after step (b′) with an acidic solution to achieve elafibranor;
• and
• d′. optionally isolating and optionally purifying elafibranor thus obtained.