2-Phenylselanyl-1,3-dienes 3-8 were prepared by a Wittig or Wittig-Horner-Emmons procedure starting from α-phenylselanylα,βunsaturated aldehydes. Ratio and configuration of each diene isomers were determined by 77 Se and 1 H 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 dihaloselenuranes occurred, yielding allenyl alcohols 12-15, allenyl carbamates 16c-19c, and 1-haloalkyl allenes 20c-22c, respectively.In particular, selenoxides play a pivotal role since the facile oxidation of alkyl phenylselenides allows the preparation of olefinic compounds and allylic alcohols under very mild conditions. 1,2 Our group was mainly involved in the studies of the reactivity of selenylated carbonyl derivatives allowing access to unsaturated, functionalized useful building-blocks 7 and their transformation into allenic alcohols via oxidation of 2-phenylselanyl-1,3-dienes. 8 These interesting selenylated dienes could also act as useful intermediates in organic synthesis, for example, as starting materials in Diels-Alder cycloaddition. 9,10 In the literature, very few preparations of 1-arylselanyl-1,3-butadienes are described: phenylselanyl alkylidene phosphoranes, phenylselanylalk-enals 11a or palladium-catalyzed cross coupling reactions. 11b A stereoselective synthesis of 1,3-dienyl selenides was re-ported by reaction of α-arylselanylvinylstannanes with vinyl halides 11c or by means of α-alkenylzirconium complexes with α-phenylselanylvinyl bromides. 11dHerein, we present a general access to 2-phenylselanyl-1,3-dienes along with an unambiguous determination of the stereochemistry by 77 Se NMR. Due to both vinylic and allylic position of the selanyl group in 2-phenylselanyl-1,3-dienes, sigmatropic rearrangements of selenoxides, selenimides, and dihalo-selenuranes were also studied, yielding, respectively, allenic alcohols, carbamates, and 1-haloalkyl allenes.
