A process for the preparation of -N-(4-(4-fluorophenyl)-6-isopropyl-5-(3-oxoprop-1-enyl)pyrimidin-2-yl)-N-methylmethanesulfonamide of formula I which comprises: (a) Treating N-(4-(4-fluorophenyl)-5-formyl-6-isopropylpyrimidin-2-yl)-N-methyl methane-sulfonamide of formula III with a compound selected from i) an unsaturated compound of formula IV wherein R 1 and R 2 are independently selected from H, alkyl, aryl or a heterocyclic moiety; Y is selected from M, MX, BR a R b and MR a R b R c, wherein M is selected from alkali, Zn, Mg, Sn and Si; X is selected from Cl, Br and I; R a, R b and R c are independently selected from X, H, C 1 -C 2 alkyl, phenyl and alkoxy; and when Y is BR a R b, then R a and R b form bidentate alkoxy; and ii) a compound selected from (R') 2 Zn, (R') 2 CuLi, (R') 2 Cu Li 2, R'R"CuLi or R'R"Cu Li 2, wherein R' is a group of formula V with R 1 and R 2 having the same structures as defined above, and R" is a heteroaryl group, in an inert solvent, optionally in the presence of a promoter, to obtain compound of formula VI; (b) oxidative cleavage of the aliphatic carbon-carbon double bond of the obtained compound of formula VI and optionally isolating intermediate of formula VII; (c) dehydration of intermediate of formula VII; and (d) isolation of compound of formula I. (a) Treating N-(4-(4-fluorophenyl)-5-formyl-6-isopropylpyrimidin-2-yl)-N-methyl methane-sulfonamide of formula III with a compound selected from i) an unsaturated compound of formula IV wherein R 1 and R 2 are independently selected from H, alkyl, aryl or a heterocyclic moiety; Y is selected from M, MX, BR a R b and MR a R b R c, wherein M is selected from alkali, Zn, Mg, Sn and Si; X is selected from Cl, Br and I; R a, R b and R c are independently selected from X, H, C 1 -C 2 alkyl, phenyl and alkoxy; and when Y is BR a R b, then R a and R b form bidentate alkoxy; and ii) a compound selected from (R') 2 Zn, (R') 2 CuLi, (R') 2 Cu Li 2, R'R"CuLi or R'R"Cu Li 2, wherein R' is a group of formula V with R 1 and R 2 having the same structures as defined above, and R" is a heteroaryl group, in an inert solvent, optionally in the presence of a promoter, to obtain compound of formula VI; i) an unsaturated compound of formula IV wherein R 1 and R 2 are independently selected from H, alkyl, aryl or a heterocyclic moiety; Y is selected from M, MX, BR a R b and MR a R b R c, wherein M is selected from alkali, Zn, Mg, Sn and Si; X is selected from Cl, Br and I; R a, R b and R c are independently selected from X, H, C 1 -C 2 alkyl, phenyl and alkoxy; and when Y is BR a R b, then R a and R b form bidentate alkoxy; and wherein R 1 and R 2 are independently selected from H, alkyl, aryl or a heterocyclic moiety; Y is selected from M, MX, BR a R b and MR a R b R c, wherein M is selected from alkali, Zn, Mg, Sn and Si; X is selected from Cl, Br and I; R a, R b and R c are independently selected from X, H, C 1 -C 2 alkyl, phenyl and alkoxy; and when Y is BR a R b, then R a and R b form bidentate alkoxy; and ii) a compound selected from (R') 2 Zn, (R') 2 CuLi, (R') 2 Cu Li 2, R'R"CuLi or R'R"Cu Li 2, wherein R' is a group of formula V with R 1 and R 2 having the same structures as defined above, and R" is a heteroaryl group, in an inert solvent, optionally in the presence of a promoter, to obtain compound of formula VI; (b) oxidative cleavage of the aliphatic carbon-carbon double bond of the obtained compound of formula VI and optionally isolating intermediate of formula VII; (c) dehydration of intermediate of formula VII; and (d) isolation of compound of formula I.