4-Ethynylbenzaldehyde, or p-ethynylbenzaldehyde, is an organic compound with the formula HC<sub>2</sub>C<sub>6</sub>H<sub>4</sub>COH. It is an ethynyl derivative of benzaldehyde, or may also be viewed as a formylated derivative of phenylacetylene.
4-Ethynylbenzaldehyde may be prepared by the Sonogashira coupling of 4-bromobenzaldehyde with trimethylsilylacetylene to form 4-((trimethylsilyl)ethynyl)benzaldehyde, followed by removal of the trimethylsilyl group with base to form 4-ethynylbenzaldehyde.
The ethynyl functionality of 4-ethynylbenzaldehyde may undergo a Sonogashira coupling with another molecule of 4-bromobenzaldehyde to form the symmetrical dialdehyde 4,4'-(ethyne-1,2-diyl)dibenzaldehyde.