Selenylated dienes: synthesis, stereochemical studies by 77Se NMR, and transformation into functionalized allenes

2-Phenylselanyl-1,3-dienes 3–8 were prepared by a Wittig or Wittig–Horner–Emmons procedure starting from α-phenylselanyl α,β-unsaturated aldehydes. Ratio and configuration of each diene isomers were determined by 77Se and 1H NMR. These dienes were then oxidized into selenoxides, which could be isolated in some cases. In THF, [2,3]-sigmatropic rearrangement of allylic selenoxides, selenimides, and dihalo-selenuranes occurred, yielding allenyl alcohols 12–15, allenyl carbamates 16c–19c, and 1-haloalkyl allenes 20c–22c, respectively.