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.
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 GaC 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 GaC 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 GaC and even more reactive GaH bonds beside peroxo groups. It decomposed at room temperature by the insertion of oxygen atoms into the GaH 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).