there are disclosed a process for producing a sulfon derivative of formula : wherein ar represents an aryl group which may be substituted , r represents a lower alkyl group and the wavy line depicted by indicates a single bond and stereochemistry relating to a double bond bound therewith is e or z or a mixture thereof , which process is characterized by reacting an aldehyde derivative of formula : with phosphonium salt of formula : in the presence of a base ; a sulfone derivative of formula and a process for producing a β - carotene using sulfone derivative of formula .