The Julia olefination (also known as the Julia–Lythgoe olefination) is the chemical reaction used in organic chemistry of phenyl sulfones (1) with aldehydes (or ketones) to give alkenes (olefins)(3) after alcohol functionalization and reductive elimination using sodium amalgam[1][2] or SmI2.[3] The reaction is named after the French chemist Marc Julia.

The utility of this connective olefination reaction arises from its versatility, its wide functional group tolerance, and the mild reaction conditions under which the reaction proceeds.
All four steps can be carried out in a single reaction vessel, and use of R3X is optional. However, purification of the sulfone intermediate 2 leads to higher yield and purity. Most often R3 is acetyl or benzoyl, with acetic anhydride or benzoyl chloride used in the preparation of 2.