Hydroxylation of an halogen addition to the carbon carbon double bond of (R)-2-hydroxy-3-enoic acids

Article abstract of DOI:10.1016/S0040-4020(01)86507-8

Various (R)-2-hydroxy-3-enoic acids and their derivatives have been subjected to epoxidations with peracids, dihydroxylations with osmium tetroxide or methylrhenium trioxide. Depending on the derivatives and reagents applied, the diastereomeric excesses (de) achieved were in the range of 8-80%. Based on the different addition mechanisms of osmium tetroxide and methylrhenium trioxide, all four possible 2,3-dihydroxy-γ-butyrolactones, i.e. (2R,3R,4R)-, (2R,3R,4S)-, (2R,3S,4R)- and (2R,3S,4S)-γ-butyrolactones with different substituents in the 4-position could be obtained. The de values of the hydrogenation products of (R)-2-hydroxy-3-methyl-4-phenyl-3E-butenoic acid or its derivatives with a nonchiral Wilkinson catalyst depended noticeably on the derivatives used. High and extremely high stereoselectivities were observed with the halolactonization of (R)-2-hydroxy-3-enoic acids with N-bromosuccinimide or iodine leading to (2S,3R,4S)-2-hydroxy-3-halogeno-γ-butyrolactones. Br₂-addition formed (2S)-2-hydroxy-3,4-dibromo carboxylic acids with stereoselectivity markedly depending on the derivatives of (R)-2-hydroxy-4-phenyl-butenoic acid applied and on the substituents at the double bond.