Published in Henry Rzepa's Blog

Sharpless epoxidation converts a prochiral allylic alcohol into the corresponding chiral epoxide with > 90% enantiomeric excess[cite]10.1021/jo00369a032[/cite],[cite]10.1021/jo00360a058[/cite]. Here is the first step in trying to explain how this magic is achieved.

References

General ChemistryCatalysisOrganic Chemistry

Reducing GaH and GaC Bonds in Close Proximity to Oxidizing Peroxo Groups: Conflicting Properties in Single Molecules

Published in Chemistry – A European Journal
Authors Werner Uhl, Mohammad Reza Halvagar, Michael Claesener

AbstractTreatment of [Li(H2Ga{CH(SiMe3)2}2)]⋅2 OEt2 (1⋅2 OEt2) with two equivalents of tert‐butyl hydrogen peroxide, H‐O‐O‐CMe3, afforded the organogallium peroxide [({(Me3Si)2HC}2Ga(OH)(OOCMe3)Li)2] (3), which possesses oxidizing peroxo groups in close proximity to reducing GaC bonds. The lithium atoms of the dimeric formula units are coordinated by both oxygen atoms of the peroxides and by two hydroxo groups. The cleavage of the GaC bond was not observed, even when an excess of H‐O‐O‐CMe3 was applied. Instead, the adduct [{(Me3Si)2HC}2Ga(OH)(OOCMe3)2Li2(HOOCMe3)] (4) was isolated, which has an intact H‐O‐O‐CMe3 molecule terminally attached to lithium. A similar structural motif was found for the compound [(LiOOCMe3)2(HOOCMe3)2] (5). The trihydrido gallanate [Li(H3Ga{CH(SiMe3)2})]⋅OEt2 (2) yielded the unique peroxide [({(Me3Si)2HC}Ga(H)(OOCMe3)2Li)2] (6) under similar conditions that possesses GaC and even more reactive GaH bonds beside peroxo groups. It decomposed at room temperature by the insertion of oxygen atoms into the GaH bonds and the formation of [({(Me3Si)2HC}Ga(OH)(OCMe3)(OOCMe3)Li)2] (7), which was isolated in a low yield. Further decomposition gave the complete degradation of all peroxo groups with the formation of a relatively complicated Li4Ga4O8 cage (8).