reaction of Wittig reagents with elemental selenium gave the corresponding selenoaldehydes which further reacted with other Wittig reagents to give the corresponding dimeric olefins in good yields. The selenoaldehydesformed afforded corresponding adducts by the reaction with dienes. These selenoaldehydes obtained by retro Diels–Alder reaction were also found to react with Wittig reagents to give the corresponding
Oxidation of 3,6-dihydro-2H-selenopyrans with an electron-withdrawing group at the 2 position proceeded via an unprecedented ring-contraction to afford selenophenes.