Complex sentence: Selenenic acids are believed to be transient intermediates in a number of reactions involving redox processes at selenium, most notably the syn-elimination of selenoxides, and the reduction of seleninic acids as well as the oxidatlon of diselenides.
Split into simpler sentences: Selenenic acids are believed to be transient intermediates in a number of redox reactions involving organoselenium compounds. Seleninic acids are also transient intermediates in the reduction of seleninic acids as well as the oxidatlon of diselenides.