Asymmetric synthesis. Part III. Stereospecific synthesis of (R)-2-hydroxy-2-phenylpropionic acid, and (R)- and (S)-2-cyclohexyl-2-hydroxy-2-phenylacetic acid. Configurational relationship between (R)(–)-2-hydroxy-2-phenylpropionic acid and (S)(+)-2-phenylpropionic acid

Abstract

Carbohydrate derivatives PhC(R)(OH)[CHOH]_n·CH₂·OH that contain an asymmetric benzylic centre of known absolute configuration are degraded to simple acids PhC(R)(OH)CO₂H. The syntheses of (R)-2-hydroxy-2-phenylpropionic acid and (R)- and (S)-2-cyclohexyl-2-hydroxy-2-phenylacetic acids are described. The configurational relationship between (R)(–)-2-hydroxy-2-phenylpropionic acid and (S)(+)-2-phenylpropionic acid is established by a novel method. N.m.r. spectroscopy is used to show that Raney nickel hydrogenolysis of 6-deoxy-1,2-O-isopropylidene-5-C-phenyl-β-L-idofuranose proceeds stereospecifically with retention of configuration and the product is degraded to (S)(+)-2-phenylpropionic acid.