The dienamine (a mixture of isomers) obtained from citral and diethylamine is converted to a mixture of citral anhydro cyclodimers by the action of weak proton-donor agents. The principal reaction product corresponds to [4 + 2]-cycloaddition of 1-diethylamino-7-methyl-3-methylene-1,6-octadiene (the minor component in the starting dienamine) to the enimmonium form of the protonated dienamine.