Novel Five- and Six-Membered Rings of Phosphorus–Selenium Heterocycles from Selenation of Amido-Schiff Bases

Woollins’
reagent, [2,4-bis­(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide],
serving as a selenating-reductive cycloaddition reagent, reacts with
nonconjugated amido-Schiff bases to give the corresponding six-membered
1,3,4-selenadiazoles via a ring-expansion accompanied by an additional
selenation/cyclization to the imine bond and CO group; meanwhile,
under the same reaction conditions, the selenation of conjugated amido-Schiff
bases leads to a series of fused heterocycles with two five-membered
rings. Eight single-crystal X-ray structures confirming the formation
of these five- and six-membered heterocycles are discussed.