| http://www.w3.org/ns/prov#value | - The present invention also provides a process for the preparation of a compound of formula (2) which comprises treating a compound of formula (A): optionally substituted by groups R2-R9, wherein X, Y, Za, Zb and groups R1, R2, R3, R4, R5, R6, R7, R8 and R9 are as defined above and R is methyl or ethyl, in mild acid solution, such as in acetic acid.
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