Stereoselective Ring Expansion of Vinyl Oxiranes: Mechanistic Insights and Natural Product Total Synthesis

What a (strain) relief! The first broadly applicable, catalytic, and stereoselective vinyl oxirane ring expansion is described (see scheme; hfacac=hexafluoroacetylacetonate). The stereoselectivity was influenced by several reaction parameters, and kinetic studies support a mechanistic proposal involving the in situ formation of a more reactive catalytic species. This ring-expansion reaction has been employed in the asymmetric total synthesis of (+)-goniothalesdiol.