The present invention relates to processes for preparing the compounds of general formula I, wherein the groups R1 and R3 are defined according to claim 1. Furthermore this inventions relates to intermediates obtained in these processes.本發明係關於製備通式I化合物之方法其中基團R1及R3如請求項1中所定義。此外本發明係關於在該等方法中所獲得之中間物。