The present invention relates to a process for the preparation of a compound of formula (I), a stereoisomer, a salt, a hydrate or a solvate thereof, comprising the step of desulfinylation of a compound of formula (II) to produce compound of formula (I); wherein: R.sup.1 and R.sup.2 are as defined in the claims, wherein said desulfinylation step is performed by continuous flow process.

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