Synthesis of a stable selenoaldehyde by self-catalyzed thermal dehydration of a primary-alkyl-substituted selenenic acid.

The unprecedented dehydration of a selenenic acid (RCH2SeOH) to a selenoaldehyde (RCH=Se) 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 [RCH2SeSe(O)CH2R], an isomer of a selenenic anhydride, and 2) subsequent β elimination of the selenenic acid from this intermediate to form a C=Se double bond, which establishes the self-catalyzed β dehydration of the selenenic acid.