Kinetic studies on the pyramidal inversion of optically active selenonium imides

Abstract

Kinetic studies were carried out on the thermal epimerization by pyramidal inversion of optically active (S)‐(−)Se‐ and (R)‐(+)Se‐4‐[(‐)‐menthyloxycarbonyl]phenyl(2′,4′,6′‐triisopropylphenyl)selenonium‐N‐toluene‐4″‐sulphonimides (1). The first‐order rate constants for the pyramidal inversion of (S)‐(−)Se‐1 and (R)‐(+)Se‐1 were determined and the activation enthalpies and entropies were calculated. A fairly large difference was found in the activation parameters between optically active (S)‐(−)Se‐1 and (R)‐(+)Se‐1, i.e. a large negative activation entropy was obtained in the case of (R)‐(+)Se‐1.

Isolation and Stereochemistry of Optically Active Selenonium Imides

“…Similarly, the rates of racemization of ( R )-(+)- 1b and ( R )-(+)- and ( S )-(−)- 1d were also studied. These results are summarized in Table together with those of diastereoisomeric selenonium imides (+)- 3 and sulfonium imides (−)- 5 and (−)- 6 . The results show that the selenonium imides are more stable than the sulfonium imides for racemization; i.e., the activation energies of the selenonium imides 1b and 1d are ca.…”