A method for the stereoselective construction of 4-alkoxy-5-alkylideneecyclopentenones by the tandem ring expansion-functionalization of 1-alkynylcyclobutenols using a palladium-mercury cocatalytic system

Article abstract of DOI:10.1021/jo00084a038

1-(1-Alkynyl)-4-methoxy-4-methyl-2-cyclobutenols, prepared by nucleophilic functionalization of cyclobutenediones, were transformed with high stereoselectivity into 4-methoxy-4-methyl-5-alkylidenecyclopentenones. The action of stoichiometric Hg(OCOCF₃)₂ and then metathesis with NaCl produced 5-(1-(chloromercurio)alkylidene)-4-methoxy-4-methyl-2-cyclopentenones which were stereospecifically functionalized by palladium-mediated allylation and hydroxybutenylation. Treatment with Br₂/DMSO led to stereospecific bromodemercuration. The 1-(1-alkynyl)-4-methoxy-4-methyl-2-cyclobutenols underwent efficient and very stereoselective tandem ring expansion-functionalizations in the presence of three different allylic chlorides and a catalyst system composed of 10% Hg(OCOCF₃)₂ and 10% PdCl₂. All products can be obtained with a stereoselectivity greater than 99:1 at the exocyclic alkene.