Reactive selenoaldehydes formed from selenenyl derivatives by 1,2-elimination and trapped in situ as cycloadducts with conjugated dienes

Abstract

Selenenyl derivatives, ZCH₂SeX, where Z is an electron-withdrawing group (Z = EtO₂C, McO₂C, PhCO, PhNHCO, or NC) and X is a leaving group (X = CN, SO₃K, CI, SO₂Tol, and N-phthalimido), react with triethylamine to form selenoaldehydes, ZCHSe, by 1,2-elimination of HX. The transient selenoaldehydes can be trapped in situ as cycloadducts with the conjugated dienes 2,3-dimethylbuta-1,3-diene, cyclopentadiene, cyclohexa-1,3-diene, the alkaloid thebaine (27), anthracene, and 9,10-dimethylanthracene. Efficient trapping (>60%) has been achieved only with cyclopentadiene and dimethylanthracene. Certain of the cycloadducts, e.g. those from dimethylbutadiene, are accompanied by lesser amounts of the cycloadducts of diselenoesters, e.g. EtO₂CCH₂SeC(Se)CO₂Et. The cycloadducts of cyclopentadiene, anthracene, and 9,10-dimethylanthracene dissociate at 80–120 °C to release the selenoaldehydes, which can be trapped in situ in high yield with dimethylbutadiene. The ease of formation and trapping, and the stereoselectivity in cycloadditions, of selenoaldehydes are compared with the corresponding properties of analogous thioaldehydes.