Selective Transformations of threo-2,3-Dihydroxy Esters

Article abstract of DOI:10.1021/jo00008a051

Two highly regio- and stereoselective transformations of threo-2,3-dihydroxy esters have been developed.In the first reaction, the α-hydroxy group is converted into a sulfonate group (tosylate or nosylate); the α-tosylates and α-nosylates are then subjected to basic conditions (K2CO3/ROH) to give erythro glycidic esters in high yield.The α-nosylates are also suitable electrophiles for azides, giving access to erythro-α-azido-β-hydroxy esters.The second reaction involves conversion of the diol esters to acetoxy bromo esters.The β-subsituent plays a key role in determining the regiochemistry since cases with β-alkyl substituents afford β-acetoxy-α-bromo esters exclusively, whereas a β-phenyl substitutent directs formation of the α-acetoxy-β-bromo ester.The acetoxy bromo esters can subsequently be converted to the threo glycidic esters (via the bromohydrin esters); selective hydrogenolysis of the bromine substituent can also be achieved.