Preparation of Vinylcyclopropanes by Sodium Mediated Reductive Isomerization of Methylenecyclopropanes

We
disclosed therein a new reaction of reductive isomerization
of methylenecyclopropanes (MCPs) to vinylcyclopropanes (VCPs). On
treatment with sodium metal in liquid ammonia, MCPs bearing a C–O
bond at allylic position undergo both a reductive cleavage of the
C–O bond and an isomerization of the C–C double bond
giving rise to VCPs. The scope of the reductive isomerization was
investigated and showed a broad applicability since various functional
groups are tolerated. MCP substrates were straightforwardly prepared
by a palladium-promoted [2 + 1] cycloaddition between norbornene derivatives
with alkynes.