B. Willemsens, A. Copmans, Dirk Beerens
2004
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Abstract
A facile and scalable method for the synthesis of 4-amino-5-chloro-2,3-dihydro-7-benzofurancarboxylic acid, an intermediate in the synthesis of the enterokinetic agent Rlo8512, has been developed. The key step in the synthesis is a zinc mediated ring closure of methyl 4-(acetylamino)-3-bromo-2-(2-bromoethoxy)-5-chlorobenzoate. The ring closure can be achieved without preliminary activation of the zinc on condition that the oxygen content in the reaction mixture is lower than 0.5%. The new process eliminates hazardous chemicals (ethyleneoxide) and low temperature reactions (-70°C, n-BuLi).