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Stereospecific ester activation in nitrite-mediated carbohydrate epimerization.
Hai Dong1, Zhichao Pei, Olof Ramström
1KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm, Sweden.
The Journal of Organic Chemistry
|April 8, 2006
Summary
The Lattrell-Dax method enables efficient carbohydrate triflate inversion. A neighboring equatorial ester group is crucial for successful nitrite-mediated substitution and inverse configuration generation.
Area of Science:
- Carbohydrate Chemistry
- Organic Synthesis
- Stereochemistry
Background:
- The Lattrell-Dax reaction provides a pathway for stereoselective synthesis of carbohydrates.
- Nitrite-mediated substitution of triflates is key for generating inverse configurations in carbohydrate structures.
Purpose of the Study:
- To investigate the epimerization of gluco- and galactopyranoside derivatives using triflation/nitrite treatment.
- To determine the influence of neighboring ester groups on the reactivity and yield of nitrite-mediated triflate inversion.
Main Methods:
- Triflation of carbohydrate derivatives followed by nitrite treatment.
- Analysis of reaction products to determine stereochemical outcomes and inversion yields.
- Comparative study of ester groups in equatorial versus axial positions.
Main Results:
- A neighboring ester group is essential for the nitrite-mediated triflate inversion reaction to occur.
- Equatorial ester groups facilitate smooth inversion, yielding allo- and gulopyranoside structures.
- Axial ester groups significantly reduce or inhibit the inversion reaction, leading to poor yields.
Conclusions:
- The stereochemical orientation of the neighboring ester group critically influences the efficiency of carbohydrate triflate inversion.
- This understanding allows for prediction and optimization of epimerization reactions, such as converting glucopyranosides to mannopyranoside epimers.