By using tandem Ru-catalysis, internal alkynes can be coupled with aldehydes for the Synthesis of Ay-unsaturated ketones. The catalyst promotes alkyne transformations With high regioselectivity) with examples: that include the differentiation of a methyl vs ethyl substituent on the alkyne. Mechanistic studies suggest that the regioselectivity results from a Selective allene formation that is governed by allylic strain.