Process for producing α,β-unsaturated aldehyde compounds

A process for producing an α,β-unsaturated aldehyde compound, comprising:

• subjecting two different aldehyde compounds to a cross condensation reaction in the presence of an amine and a protonic acid having 6 to 20 carbon atoms or a salt thereof;
• wherein the two different aldehyde compounds are aldehyde compound I and aldehyde compound II represented by formula (I) and formula (II) respectively
• R1—CHO (I)
• R2—CHO (II)
• wherein
• R1 and R2 are different;
• R1 is a linear or branched alkyl group having 6 to 20 carbon atoms, a linear or branched alkenyl group having 6 to 20 carbon atoms, or an alicyclic structure-containing group having 6 to 20 carbon atoms;
• and R2 is a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkenyl group having 3 to 6 carbon atoms, or an alicyclic structure-containing group having 3 to 6 carbon atoms;
• or
• R1 is an aromatic ring structure-containing group having 6 to 20 carbon atoms, or a heterocyclic structure-containing group;
• and R2 is a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, or a linear or branched alkenyl group having 3 to 10 carbon atoms;
• and
• when the aldehyde compound II is HCHO, the resultant α,β-unsaturated aldehyde compound is a compound represented by formula (III-a)
• wherein R1a—C is a residual group of R1 in the formula (I) which is obtained by removing two hydrogen atoms bonded to a carbon atom being located at the α position of R1 therefrom;
• and
• when the aldehyde compound II is an aldehyde compound other than HCHO, the resultant α,β-unsaturated aldehyde compound is a compound represented by formula (III-b)
• wherein R2a—C is a residual group of R2 in the formula (II) which is obtained by removing two hydrogen atoms bonded to a carbon atom being located at the α position of R2 therefrom, and R1 is as defined in formula (I).