Medium ring ethers via [1,2]-shift of acetal-derived oxonium ylides

Article abstract of DOI:10.1016/S0040-4039(98)00856-9

Cyclic acetals and ketals with pendant diazoketones rearranged to O- bridged medium ring in the presence of catalytic Rh₂(OAc)₄ or Cu(hfacac)₂. This process proceeds via fused bicyclic oxonium ylides which undergo [1,2]- shift reactions. The observation of efficient migration by alkyl substituted carbons lacking any conjugating groups is especially notable. Overall, this chemistry furnishes functionalized medium ring ethers in a few steps from simple precursors.