Stereoisomers/stereomutation

When the unsaturated acetal 26 was reacted with superacid at — 60°C and irradiated, a photostationary state is observed consisting of the two stereoisomers 26a and 26b (Scheme 4).21 Evaluation of the kinetics of stereomutation shows good first order kinetics, and the rate constant increases with acidity. Based on the kinetics results, it was proposed that protonation of the carboxonium group of 26b leads to the dication (27), and this facilitates isomerization through delocalization of the positive charge. 

Studies of hypervalent phosphorus compounds in biological phosphoryl transfer reactions include the preparation of novel anti-apicophilic penta-coordinated phosphoranes with frozen stereomutation using bulky biden-tate ligands. Kinetic studies have enabled the activation enthalpy of the stereomutation of an 0-equatorial phosphorane to its O-apical stereoisomer to be calculated. The involvement of hexacoordinated phosphoranes in phosphate transfer reactions has been clarified by theoretical calculations as well as in vitro studies. Applications of hexacoordinated compounds as catalysts have also been described. 

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