4-Ethynylbenzaldehyde, or p-ethynylbenzaldehyde, is an organic compound with the formula HC2C6H4COH.

[2] 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.

[3] 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.

[3]