Cinchona alkaloid derivatives, their process of preparation and their use as catalysts

摘要

The present invention provides a process for preparing a substantially stereochemically pure compound of formula (I), or a salt thereof wherein R₁ and R₂ are independently selected from the group consisting of H, -CH₂-CH₃, and -CH=CH₂, the process comprising the step of demethylating the corresponding methylated compound of formula (II) in the presence of an alkaline or alkaline earth metal (C₁-C₁₀) alkylthiolate salt and a polar aprotic solvent.