Ruthenium-Catalyzed Cycloaddition between Propargylic Alcohols and Cyclic 1,3-Dicarbonyl Compounds via an Allenylidene Intermediate

Thiolate-bridged diruthenium complexes such as [Cp*RuCl(μ2-SR)2RuCp*Cl] (Cp* = η5-C5Me5; R
= Me, nPr, iPr) and [Cp*RuCl(μ2-SiPr)2RuCp*(OH2)]OTf (OTf = OSO2CF3) promote the cycloaddition
between propargylic alcohols and cyclic 1,3-dicarbonyl compounds to give either the corresponding
4,6,7,8-tetrahydrochromen-5-ones or 4H-cyclopenta[b]pyran-5-ones in high yields with complete
regioselectivity. This catalytic cycloaddition provides a simple and one-pot synthetic protocol for a
variety of substituted chromenones and cyclopenta[b]pyranones.