Synthesis of a Stable Selenoaldehyde by Self‐Catalyzed Thermal Dehydration of a Primary‐Alkyl‐Substituted Selenenic Acid

The unprecedented dehydration of a selenenic acid (RCH 2 SeOH) to a selenoaldehyde (RCHSe) has been demonstrated. A primary‐alkyl‐substituted selenenic acid was synthesized for the first time by taking advantage of a bulky cavity‐shaped substituent. Upon heating in solution, the selenenic acid underwent thermal dehydration to produce a stable selenoaldehyde, which was isolated as stable crystals and crystallographically characterized. Investigation of the reaction mechanism revealed that this β dehydration reaction involves two processes, both of which reflect the characteristics of a selenenic acid: 1) dehydrative condensation of two molecules of selenenic acid to generate a selenoseleninate intermediate [RCH 2 SeSe(O)CH 2 R], an isomer of a selenenic anhydride, and 2) subsequent β elimination of the selenenic acid from this intermediate to form a CSe double bond, which establishes the self‐catalyzed β dehydration of the selenenic acid.