| 摘要 |
The present invention is concerned with a novel process for the preparation of compounds of formula (I) wherein R1, R2 and X are as defined in the specification, comprising cyclocarbonylation of a compound of formula (II) wherein R1, R2, R3 and X are as defined in the specification, to produce a compound of formula (III) wherein R1, R2, R4 and X are as defined in the specification, followed by saponification.
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