Process for preparing chiral 2,3-dihydrothiazolo[3,2-A] pyrimidin-4-ium compounds

A process for preparing S-containing pyrimidinium compound of formula X

• wherein
• C* is an asymmetric carbon atom of S or R-configuration;
• R1 is C1-C4-alkyl, C3-C6-cycloalkyl, C2-C4-alkenyl, or —CH2-phenyl, which groups are unsubstituted or substituted with halogen or C1-C4-alkyl;
• R2 is a 5- or 6-membered saturated, partially unsaturated or aromatic carbo- or heterocyclic ring, wherein the ring is unsubstituted or substituted with R2a;
• Het is selected from D-1, D-2, and D-3:
• wherein
• Ra is each independently Ra is halogen, C1-C4-haloalkyl, C1C4-alkoxy, C1-C4-alkylthio, or phenyl;
• n is 0, 1 or 2;
• and
• # denotes the bond in formula X;
• R2a is halogen, C1-C6-haloalkyl, C1-C6-haloalkoxy, ORc, C(═O)ORc, C(═O)NRbRc, phenyl, or pyridyl, which is unsubstituted or substituted with halogen, C1-C6-haloalkyl or C1-C6-haloalkoxy;
• Rb is hydrogen, C1-C6-alkyl, C1-C6-haloalkyl, C1-C6-alkoxy, or C1-C6-haloalkoxy;
• and
• Rc is hydrogen, C1-C4-alkyl, C1-C4-haloalkyl, or C1-C6 cycloalkyl;
• wherein two geminally bound groups RcRb together with the atom to which they are bound, may form a 3- to 7-membered saturated, partially unsaturated or aromatic heterocyclic ring;
• comprising at least the step of,
• (E) reacting the compound of formula VII,
• wherein
• C* is an asymmetric carbon atom of S or R-configuration;
• Het is as defined in compound of formula X;
• with R1NCS, wherein R1 is C1-C4-alkyl, C3-C6-cycloalkyl, C2-C4-alkenyl or —CH2-phenyl, which groups unsubstituted or substituted by halogen or C1-C4-alkyl;
• in the presence of a base,
• to obtain a compound of formula VIII,
• wherein
• C* and Het are as defined in the compound of formula VII;
• R1 is as defined herein;
• and further reacting the compound of formula VIII to obtain the compound of formula X.