Process for the preparation of pyrazolopyrimidinones
There is provided a process for the production a compound of general formula I: wherein A, R 1 , R 2 , R 3 and R 4 have meanings given in the description, which process comprises the dehydrogenation of a compound of general formula II,
1. A compound of formula II,
wherein
A represents CH or N;
R 1 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, OR 5 , C(O)R 6 , C(O)OR 7 , C(O)NR 8 R 9 , NR 10a R 10b and SO 2 NR 11a R 11b ;
R 2 and R 4 independently represent lower alkyl;
R 3 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;
R 5 , R 6 , R 7 , R 8 , R 9 , R 11a and R 11b independently represent H or lower alkyl;
R 10a and R 10b either independently represent, H or lower alkyl or, together with the nitrogen atom to which they are attached, represent azetidinyl, pyrollidinyl or piperidinyl.
2. A compound of formula III,
wherein A, R 3 and R 4 are as defined in claim 1 .
3. A compound of formula VI,
wherein R 3 and R 4 are as defined in claim 1 .