Vinyl Ketones as Alkyne Partners

What happens when p-hydrogcn elimination in the ruthenacyclic intermediate 45 is preduded, as in the case when vinyl ketones are the alkene partners (Equation 1.55) Given the extraordinary ability of Ru to interconvert easily among numerous oxidation states, one can imagine that the Ru can activate the double bond towards additions. For example, in the presence of water, protonation at the carbon (5 to Ru in the ruthenacyclopentene followed by nucleophilic addition of hydroxide can lead to 1,5-diketone formation. Indeed, terminal alkynes undergo smooth three-component coupling to form 1,5-diketones as shown in Equation 1.56 [52]. 

In the case that the alkyne partner contains a propargylic hydroxyl group, the flexibility of Ru to form higher oxidation states may allow ionization of this hydroxyl group followed by recombination as shown in Equation 1.57, ruthenacyde 46 to 47 to 48. Indeed, the simple addition of propargyl alcohol 49 and methyl vinyl ketone produces the nicely functionalized 1,5-diketone 50 (Equation 1.58) [53], Such functionality sets the stage well for further elaborations. 

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