title: Crystal structure of (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman.
abstract: The title compound, C11H11FO2, is a building block in the synthesis of the active pharmaceutical ingredient dl-nebivolol. The synthesis starting from the enanti-omerically pure (R)-6-fluoro-4-oxo-3,4-di-hydro-2H-chromene-2-carb-oxy-lic acid resulted in a mixture of two stereoisomers, namely (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman and (R)-6-fluoro-2-[(R)-oxiran-2-yl]chroman. The mixture was separated by column chromatography but only one stereoisomer crystallized. The X-ray structure analysis revealed that the solid consisted of the R,S isomer. A similar procedure was repeated for (S)-6-fluoro-4-oxo-3,4-di-hydro-2H-chromene-2-carb-oxy-lic acid and, in this case, the S,R isomer was produced as a crystalline solid. Thus, all four stereoisomers of the title epoxide were obtained and their absolute configuration was assigned. The crystal studied was refined as an inversion twin.
authors.affiliation: Universite de Bourgogne, ICMUB-UMR6302, 9 avenue Alain Savary, 21000 Dijon, France.
authors.forename: Yoann
authors.initials: Y
authors.lastname: Rousselin
authors.affiliation: CordenPharma-Synkem, 47 rue de Longvic, 21301 Chenove, France.
authors.forename: Hugo
authors.initials: H
authors.lastname: Laureano
authors.affiliation: CordenPharma-Synkem, 47 rue de Longvic, 21301 Chenove, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Clavel
keywords: absolute configuration; crystal structure; nebivolol