Density functional theory computations of the Cu-catalyzed ring expansion of vinyloxiranes was found to be mediated by a dual Cu(I)-catalyst mechanism. Overall, the reaction involves a monomeric Cu(I)-catalyst, but a single key step, the Cu migration, requires two Cu(I)-catalysts for the transformation. This dual-Cu step was found to be a true two Cu(I)-transition state rather than a mono Cu(I)-transition state in the presence of an adventitious, spectator Cu(I). Interestingly, the reductive elimination is rate-determining for the major diastereomeric product, while the Cu(I)-migration step was rate-determining for the minor. Thus, while the reaction required dual Cu(I)-activation to proceed, kinetically, the presence of the dual-Cu(I) step is untraceable. The diastereospecificity of this reaction was controlled by the Cu migration step. Suprafacial migration is favored over antarafacial migration due to the distorted Cu p�allyl in the latter.

Mechanism and the origins of stereospecificity in copper catalyzed ring expansions of vinyl oxiranes: A traceless dual transition metal-mediated process

245th National Meeting (2013)

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