Process for the preparation of pyrazolopyrimidinones

A compound of formula II,

• wherein
• A represents CH or N;
• R1 represents H, lower alkyl (which alkyl group is optionally interrupted by O), Het, alkylHet, aryl or alkylaryl, which latter five groups are all optionally substituted (and/or, in the case of lower alkyl, optionally terminated) by one or more substituents selected from halo, cyano, nitro, lower alkyl, OR5, C(O)R6, C(O)OR7, C(O)NR8R9, NR10aR10b and SO2NR11aR11b;
• R2 and R4 independently represent lower alkyl;
• R3 represents lower alkyl, which alkyl group is optionally interrupted by oxygen;
• Het represents an optionally substituted four- to twelve-membered heterocyclic group, which group contains one or more heteroatoms selected from nitrogen, oxygen and sulfur;
• R5, R6, R7, R8, R9, R11a and R11b independently represent H or lower alkyl;
• R10a and R10b either independently represent, H or lower alkyl or, together with the nitrogen atom to which they are attached, represent azetidinyl, pyrollidinyl or piperidinyl.