Synthesis of β-C-galacto-Pyranosides with Fluorine on the Pseudoanomeric Substituent
摘要:
beta-C-galacto-Pyranosides with CHF and CF2 substitutes for the glycosidic oxygen were prepared through a four-step sequence starting from a central 1-thio-1,2-O-isopropylidene acetal alcohol and different alpha-fluoro- and alpha,alpha-difluoro acids. The key step in the synthesis is the oxocarbenium cyclization of an intermediate enol ether-thioacetal to a C1-substituted glycal.
Asymmetric epoxidation of fujorinated allylic alcohols
摘要:
The asymmetric epoxidation of an alpha, beta-difluoro primary allylic alcohol, and of two alpha-fluoro secondary allylic alcohols follows the pattern known with non fluorinated analogs. The fluoro epoxides thus formed can be transformed into chiral alpha-ketols and into an alpha-fluoroacid.
Asymmetric hydrogenation of (Z)-2-fluoro-2-alkenoic acid, (Z)-1a and (Z)-1b, was carried out, employing Ru2Cl4(binap)2(NEt3) as a catalyst to afford 2-fluoroalkanoic acids, 2a and 2b, having high enantiomeric purities (up to 90% e.e.) When the (R)-binap catalyst was used, not only (Z)-1a but (E)-1a was hydrogenated smoothly to give (R)-2a with comparable asymmetric induction.
Diastereoselective fluorination of chiral imide enolates using n-fluoro-o-benzenedisulfonimide (nfobs)
作者:Franklin A. Davis、Wei Han
DOI:10.1016/s0040-4039(00)91883-5
日期:1992.2
α-Fluoro acids (78–90% ee) and β-fluoro alcohols (89–>95%ee) of well defined stereochemistry are prepared via the diastereoselective fluorination of chiral imide enolates with NFOBS (3).