Alkynes typically undergo the same addition reactions as alkenes, and these reactions may occur consecutively. However, the hydration of alkynes is exceptional and demands an Hg(II) catalyst. The initial product is an enol, which rearranges to a ketone through tautomerism.
To prevent the hydroboration of terminal alkynes at the alkenylboron intermediate stage, modified dialkylboranes, especially dicyclohexylborane, are employed. The oxidation of the resulting alkenylboranes leads to enols, which undergo tautomerization to aldehydes.