Vito Capriati’s favorite structure is:

α-Lithiated oxirane

Lithiated_epoxide

Source: Chemical Science 2014, 5, 528-538

Why

This is the first crystallographic evidence for the structure of a highly reactive lithiated aryloxirane (t½ = 1.6 s at 157 K in THF). All operations were carried out under a nitrogen atmosphere at the temperature of 100 K. α-Lithiated oxiranes have long considered “fleeting” intermediates in the reaction of epoxides with strong bases, but have nowadays proven to be key synthons for asymmetric synthesis. They are small-ring heterocycles carrying a peculiar polarized Li-C bond which gives them the character of “carbenoids”, thereby exhibiting an amphiphilic behaviour, that is a nucleophilic as well as an electrophilic reactivity. In spite of their widespread use in synthetic strategies, however, information about the reactivity and structural features of these species were lacking before publishing these data. Indeed, It was as well long postulated that was an alkoxy carbene, in equilibrium with the lithiated epoxide, responsible of the carbene-like reactivity observed under certain experimental conditions. The knowledge of the solution and the solid structure of these intermediates may set the scene for future development in the field of α-lithiated epoxides and for controlling stereochemistry in C–C bond forming reactions onto an oxirane moiety. —Vito Capriati


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