Hydroxyalkynes

Hydroxyalkynes are organic compounds that contain both a hydroxyl group (-OH) and a carbon–carbon triple bond (alkyne) within the same molecule. They are commonly referred to as alkynyl alcohols, with propargyl alcohol (HO-CH2-C≡CH) being the simplest example.

Structure and scope: Hydroxyalkynes can be terminal or internal. In propargyl alcohols the hydroxyl is on the carbon adjacent to the alkyne, but more generally the hydroxyl may appear on a side chain or on a carbon neighboring the alkyne, giving a range of substitution patterns around the triple bond.

Preparation: The most common preparation route is the nucleophilic addition of a metal acetylide to an aldehyde or formaldehyde, followed by aqueous workup, to yield propargyl alcohols (for example, formaldehyde plus sodium acetylide gives propargyl alcohol). Other hydroxyalkynes can be accessed by propargylation of alcohols, or via transformations of alkynyl ketones or alkynyl halides that introduce the hydroxyl-bearing carbon.

Reactivity and applications: The hydroxyl group provides a handle for further functionalization, such as ester or ether formation and various protection strategies, and it can engage in hydrogen bonding. The alkyne moiety enables a wide range of classic transformations, including hydrogenation, halogenation, hydration, and cycloadditions. In particular, hydroxyalkynes participate in copper-catalyzed azide–alkyne cycloadditions (CuAAC) and other click-chemistry reactions, making them valuable intermediates in medicinal chemistry, natural product synthesis, and polymer chemistry as building blocks or crosslinkable units.

Notes: Terminal hydroxyalkynes can be relatively acidic at the terminal hydrogen and may be sensitive to bases and heat, requiring careful handling and storage for some substrates.