Process for the preparation of a key intermediate of siponimod

A process for preparing a compound of formula (I)

• the process comprising :
• a) converting a compound of formula (II) into a compound of formula (III), via a formation of intermediate compound (IIa) in suitable solvents:
• where R is mesyl or tosyl and R1 is a group of formula
• where R2 and R3, each independently, represent hydrogen, C1-C4-alkyl, halogen, nitro or R2 and R3 together form an aliphatic or aromatic, 5 to 7 membered ring;
• b) converting the thus obtained compound of formula (III) into a compound of formula (IV) by a hydrolysis of the R1 group and a subsequent reaction with 3-ethyl-2-hydroxymethylacetophenone, via a formation of intermediate compound (IIIa) according to the following scheme, in suitable solvents:
• c) converting the compound of formula (IV) into the compound of formula (I), in the presence of metal catalysts and an oxidizing agent, upon protection of the hydroxy group, introduction of the cyclohexyl group and deprotection of the hydroxy group, via formation of intermediate compounds (IVa), (IVb), (IVc) according to the following scheme in suitable solvents, where R4 is a protecting group of the hydroxy group:
• wherein some or all of the intermediate compounds (IIa), (IIIa), (IVa), (IVb), and (IVc) are not isolated from the reaction crude and/or purified.