Soluble Lanthanides as Mediators of the Stork–Danheiser Transposition Reaction

The reaction of organometallic reagents with vinylogous esters (Stork–Danheiser transposition) provides direct access to 3-substituted cyclic enones. However, the reaction typically fails with sterically hindered aryl or alkyl nucleophiles due to competing enolization. Cerium(III) chloride and other lanthanide salts have traditionally been used to mitigate the basicity and enhance the nucleophilic behavior of challenging nucleophiles. Yet, in our experience, using CeCl3 as a mediator of the Stork–Danheiser transposition resulted in reproducibility issues. We describe herein the application of organic-soluble lanthanides (LnCl3/R4NX and LnCl3·2LiCl) to promote the Stork–Danheiser transposition of several classes of organomagnesium reagents.