alpha , beta -Unsaturated aldehydes and ketones are prepared by reaction of an arylseleninic anhydride with an aldehyde or ketone having at least one hydrogen atom in the alpha -position which is or can be in the syn-configuration with respect to at least one hydrogen atom in the said beta -position. The ketones used as starting material especially include perhydrophenanthrene ketones such as steroid ketones and the arylseleninic anhydride used may for example be benzeneseleninic anhydride.
