Selective transformations of threo-2,3-dihydroxy esters
摘要:
Two highly regio- and stereoselective transformation of threo-2,3-dihydroxy esters have been developed. In the first reaction, the alpha-hydroxy group is converted into a sulfonate group (tosylate or nosylate); the alpha-tosylates and alpha-nosylates are then subjected to basic conditions (K2CO3/ROH) to give erythro glycidic esters in high yield. The alpha-nosylates are also suitable electrophiles for azides, giving access to erythro-alpha-azido-beta-hydroxy esters. The second reaction involves conversion of the diol esters to acetoxy bromo esters. The beta-substituent plays a key role in determining the regiochemistry since cases with beta-alkyl substituents afford beta-acetoxy-alpha-bromo esters exclusively, whereas a beta-phenyl substituent directs formation of the alpha-acetoxy-beta-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.
An Efficient and Practical Method for Olefin Dihydroxylation
作者:Zhi-bin Luo、Jimin Xie、Hong-fei Lu、Chen Zhao
DOI:10.1055/s-0035-1562783
日期:——
the dihydroxylation of various olefin derivatives with commercial KMnO4 as the oxidant in the presence of a quaternary ammonium salt. This practical procedure is suitable for large-scale production of cis-dihydroxy compounds, even those bearing primary and secondary alcohol groups, without overoxidation. An efficient and economic procedure was developed for the dihydroxylation of various olefin derivatives