440
N. Paul
compounds. In spite of all precautions, the reaction atmosphere often creates a portal
that leads to racemization. To reach the target, a chemist is left with two options.
Either by designing a method that perfectly proceeds through a specific reaction
route that selectively siphoned specific chiral molecule or choosing a second option
consisting of meticulous separation method that is able to separate two enantiomers.
The second method is termed kinetic resolution (Martin et al. 1981). In 1980, K.
B. Sharpless and T. Katsuki introduced a breakthrough epoxidation process which
efficiently satisfies both criteria (Katsuki and Sharpless 1980). In the present context,
origin of resolution is attempted to realize covering a model study of transition structure of the epoxidation based on data available on kinetic resolution method (Gao
et al. 1987). Two enantiomeric allylic alcohols constitute two diastereotopic transition states with considerably higher difference of G
= . This difference is reflected
in relative rate difference, making separation of pure enantiomers feasible.
2 Experimental Section of Sharpless Epoxidation
Katsuki et al. reported a reaction kettle is charged with dichloromethane (DCM)
in ice-cold (−20 °C) condition. Titanium (IV) tetraisopropoxide (1 equivalent), (+)
DIPT (1.2 equivalent), 1 equivalent amount of racemic allyl alcohol, and 2 equivalent
TBHP are injected by a syringe and stirred in ice-cold condition. After completion of
the reaction, this cold mixture is introduced to another precooled (−20 °C) acetone–
water mixture. The homogeneous solution is kept for a stipulated period of time
(Katsuki and Sharpless 1992). Tartrate hydrolysis and subsequent chromatographic
separation resolve enantiomerically pure epoxide.
2.1 Description of Produced Enantioselective Epoxide
with Specific Orientation
In Scheme 1, epoxide ring and lowest priority atom (hydrogen) of adjacent chiral
centre are considered for Erythro (E) and Threo (T) designation.
3 Results and Discussion
Many instances are demonstrated by K. B. Sharpless, only four instances are considered in this article. The percentage of allylic alcohol consumption during epoxidation
is not exactly known yet for some Z-alkenes, this is reported up to 55 ± 1%. In Table
1, optical purity of epoxides and their erythro–threo orientation related to Sharpless
asymmetric epoxidation are highlighted.
N. Paul
compounds. In spite of all precautions, the reaction atmosphere often creates a portal
that leads to racemization. To reach the target, a chemist is left with two options.
Either by designing a method that perfectly proceeds through a specific reaction
route that selectively siphoned specific chiral molecule or choosing a second option
consisting of meticulous separation method that is able to separate two enantiomers.
The second method is termed kinetic resolution (Martin et al. 1981). In 1980, K.
B. Sharpless and T. Katsuki introduced a breakthrough epoxidation process which
efficiently satisfies both criteria (Katsuki and Sharpless 1980). In the present context,
origin of resolution is attempted to realize covering a model study of transition structure of the epoxidation based on data available on kinetic resolution method (Gao
et al. 1987). Two enantiomeric allylic alcohols constitute two diastereotopic transition states with considerably higher difference of G
= . This difference is reflected
in relative rate difference, making separation of pure enantiomers feasible.
2 Experimental Section of Sharpless Epoxidation
Katsuki et al. reported a reaction kettle is charged with dichloromethane (DCM)
in ice-cold (−20 °C) condition. Titanium (IV) tetraisopropoxide (1 equivalent), (+)
DIPT (1.2 equivalent), 1 equivalent amount of racemic allyl alcohol, and 2 equivalent
TBHP are injected by a syringe and stirred in ice-cold condition. After completion of
the reaction, this cold mixture is introduced to another precooled (−20 °C) acetone–
water mixture. The homogeneous solution is kept for a stipulated period of time
(Katsuki and Sharpless 1992). Tartrate hydrolysis and subsequent chromatographic
separation resolve enantiomerically pure epoxide.
2.1 Description of Produced Enantioselective Epoxide
with Specific Orientation
In Scheme 1, epoxide ring and lowest priority atom (hydrogen) of adjacent chiral
centre are considered for Erythro (E) and Threo (T) designation.
3 Results and Discussion
Many instances are demonstrated by K. B. Sharpless, only four instances are considered in this article. The percentage of allylic alcohol consumption during epoxidation
is not exactly known yet for some Z-alkenes, this is reported up to 55 ± 1%. In Table
1, optical purity of epoxides and their erythro–threo orientation related to Sharpless
asymmetric epoxidation are highlighted.