Mild conversion of propargylic alcohols to α,β-unsaturated enones in ionic liquids (ILs); a new 'metal free' life for the Rupe rearrangement

A mild and selective transition metal free protocol for the conversion of propargylic alcohols to cyclic and acyclic α,β-unsaturated enones via the Rupe rearrangement is reported. The method utilizes the Brønsted acidic ionic liquid [BMIM-SO3H][OTf] as catalyst and [BMIM][PF6] as solvent and offers the potential for recycling and reuse of the IL solvent. The feasibility to synthesize bicyclic fused cyclopentenone derivatives via a Rupe → Aldol → Nazarov sequence utilizing this protocol has also been demonstrated.