A METHOD FOR THE STEREOSELECTIVE CONSTRUCTION OF 4-ALKOXY-5-ALKYLIDENECYCLOPENTENONES BY THE TANDEM RING EXPANSION-FUNCTIONALIZATION OF 1-ALKYNYLCYCLOBUTENOLS USING A PALLADIUM-MERCURY COCATALYTIC SYSTEM

1-(1-Alkynyl)-4-methoxy-4-methyl-2-cyclobutenols, prepared by nucleoph ilic functionalization of cyclobutenediones, were transformed with hig h stereoselectivity into 4-methoxy-4-methyl-5-alkylidenecyclopentenone s. The action of stoichiometric Hg(OCOCF3)(2) and then metathesis with NaCl produced o)alkylidene)-4-methoxy-4-methyl-2-cyclopentenones whic h were stereospecifically functionalized by palladium-mediated allylat ion and hydroxybutenylation. Treatment with Br-2/DMSO led to stereospe cific bromodemercuration. The 1-(1-alkynyl)-4-methoxy-4-methyl-2-cyclo butenols underwent efficient and very stereoselective tandem ring expa nsion-functionalizations in the presence of three different allylic ch lorides and a catalyst system composed of 10% Hg(OCOCF3)(2) and 10% Pd Cl2. All products can be obtained with a stereoselectivity greater tha n 99:1 at the exocyclic alkene.