Facile Diels-Alder dimerisation of a vinyloxepin synthesised using intramolecular ene-yne metathesis

The partially-protected D-lyxose derivative 4 was converted into the thioether-substituted lactol 6, which was subjected to Ohira–Bestmann alkynylation, O-allylation and ene–yne metathesis to give a bicyclic vinyloxepin. This underwent high-yielding and completely regio-and stereo Diels–Alder dimerisation at ambient temperature. X-Ray crystallographic analysis of the dimer revealed unexpectedly that epimerisation at the sugar C2-position had taken place during the alkynylation step.