Ruthenium/TFA-Catalyzed Coupling of Activated Secondary Propargylic Alcohols with Cyclic 1,3-Diones: Furan versus Pyran Ring Formation

A catalytic system consisting of the 16-electron allyl-ruthenium(II) complex [Ru(η3-2-C3H4Me)(CO)(dppf)][SbF6] (dppf = 1,1′-bis(diphenylphosphino)ferrocene) and trifluoroacetic acid (TFA) has been used to promote the coupling between secondary propargylic alcohols and cyclic 1,3-diketones. The nature of the resulting products was found to be dependent on the ring size of the dicarbonyl compound employed. Thus, whereas 6,7-dihydro-5H-benzofuran-4-ones have been selectively obtained starting from 1,3-cyclohexanediones, via furan-ring formation, the use of 1,3-cyclopentanedione leads instead to 6,7-dihydro-4H-cyclopenta[b]pyran-5-ones via a pyran-ring formation process.